Microcomputer with self-test of macrocode

ABSTRACT

A microcomputer device contains a CPU with an arithmetic/logic unit and data/address registers on a single semiconductor integrated circuit having on-chip macrocode and microcode storage. A macrocode word is fetched from an on-chip ROM and stored in an instruction register in the CPU, then a sequence of microcode words is fetched from the microcode store based on this macrocode word. A check-code based on some function of all macrocode bits is stored in on-chip ROM upon manufacture. To test a device after fabrication is complete, a test program (resident in ROM or downloaded into on-chip RAM) is executed to address all bytes of macrocode and perform some cummulative function on it via the ALU to see if the same check-code is produced. If so, an output indicates a good unit.

BACKGROUND OF THE INVENTION

This invention relates to integrated semiconductor devices and systems, and more particularly to features used in an electronic digital processing system of the single-chip microprocessor or microcomputer form.

A microprocessor device is a central processing unit or CPU for a digital processor which is contained in a single semiconductor integrated circuit, usually fabricated by "MOS/LSI" technology, as shown in U.S. Pat. No. 3,757,306 issued to Gary W. Boone and assigned to Texas Instruments. The Boone patent shows an 8-bit CPU on a chip including a parallel ALU, registers for data and addresses, an instruction register and a control decoder, all interconnected using a bidirectional parallel bus. U.S. Pat. No. 4,074,351, issued to Gary W. Boone and Michael J. Cochran, assigned to Texas Instruments, shows a single-chip "microcomputer" type device which contains a 4-bit parallel ALU and its control circuitry, with on-chip ROM and RAM for program and data storage. The term microprocessor usually refers to a device employing external memory for program and data storage, while the term microcomputer refers to a device with on-chip ROM and RAM for program and data storage; the terms are also used interchangeably, however, and are not intended as restrictive as to this invention.

Subsequent to 1971 when U.S. Pat. Nos. 3,757,306 and 4,074,351 were originally filed, many improvements have been made in microprocessors and microcomputers to increase the speed and capability of these devices and reduce the cost of manufacture, providing more circuitry in less space, i.e., smaller chip size. Improved photolithographic techniques allow narrower line width and higher resolution, providing added circuit density, but circuit and system improvements also contribute to the goals of increased performance with smaller chip size. Some of these improvements in microprocessors are disclosed in the following U.S. Patents, all assigned to Texas Instruments: Nos. 3,991,305 issued to Edward R. Caudel and Joseph H. Raymond Jr.; 4,156,927 issued to David J. McElroy and Graham S. Tubbs; 3,934,233 issued to R. J. Fisher and G. D. Rogers; 3,921,142 issued to J. D. Bryant and G. A. Hartsell; 3,900,722 issued to M. J. Cochran and C. P. Grant; 3,932,846 issued to C. W. Brixey et al; 3,939,335 issued to G. L. Brantingham, L. H. Phillips and L. T. Novak; 4,125,901 issued to S. P. Hamilton, L. L. Miles, et al; 4,158,432 issued to M. G. VanBavel; 3,757,308 and 3,984,816.

Additional examples of microprocessor and microcomputer devices in the evolution of this technology are described in publications. In Electronics, Sept. 25, 1972, p. 31-32, a 4-bit P-channel MOS microcomputer with on-chip ROM and RAM is shown which is similar to U.S. Pat. No. 3,991,305. Two of the most widely used 8-bit microprocessors like that of U.S. Pat. No. 3,757,306 are described in Electronics, Apr. 18, 1974 at pp. 88-95 (the Motorola 6800) and pp. 95-100 (the Intel 8080). A microcomputer version of the 6800 is described in Electronics, Feb. 2, 1978 at pp. 95-103. Likewise, a single-chip microcomputer version of the 8080 is shown in Electronics, Nov. 25, 1976 at pp. 99-105 and a 16-bit microprocessor evolving from the 8080 is described in Electronics, Feb. 16, 1978, pp. 99-104. Another single-chip microcomputer, the Mostek 3872, is shown in Electronics, May 11, 1978, at pp. 105-110. An improved version of the 6800 is disclosed in Electronics, Sept. 17, 1979 at pp. 122-125, while a 16-bit microprocessor identified as the 68000 which evolved from the 6800 is described in Electronic Design, Sept. 1, 1978 at pp. 100-107.

The technology of integrated circuit design and manufacture has progressed to a point where virtually any electronic system having digital processing or control functions can employ a microcomputer or microprocessor chip. The cost of designing and manufacturing the devices is a limiting factor, however. Semiconductor manufacturing is oriented toward production of large quantities of a single device type, rather than production of a few of many different specialty items, and so to be economical a chip design must be adaptable for a wide variety of uses, not only by changing the ROM code but also by providing many input/output options and similar features. Thus, a device as in U.S. Pat. No. 3,991,305 has been manufactured in quantities of millions of units for many different electronic calculators, electronic games, appliance controllers, and the like. Not only the semiconductor manufacturing cost is minimized by use of the same device, but also the design cost is minimized because very little circuit design is needed (only external to the chip) and the programming effort employs an instruction set and commonly-used subroutines and algorithms in which a high level of experience is acquired. Nevertheless, the design cost for using a microcomputer device in a new application can be prohibitive even though only assembly language programming is needed; this software cost is unduly high because of the number of different and incompatible programming languages used on the wide variety of device types.

It is the principal object of this invention to provide an improved microcomputer or microprocessor device which is adaptable for a wide variety of uses but yet is constructed to facilitate low-cost manufacture and to minimize programming costs.

Another object is to provide lower manufacturing costs for a microprocessor or microcomputer device by employing a self-test feature.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention a microcomputer device contains a CPU with an arithmetic/logic unit and data/address registers on a single semiconductor integrated circuit having on-chip macrocode and microcode storage. A macrocode word is fetched from an on-chip ROM and stored in an instruction register in the CPU, then a sequence of microcode words is fetched from the microcode store based on this macrocode word. A check-code based on some function of all macrocode bits is stored in on-chip ROM upon manufacture. To test a device after fabrication is complete, a test program (resident in ROM or downloaded into on-chip RAM) is executed to address all bytes of macrocode and perform some cummulative function on it via the ALU to see if the same check-mode is produced. If so, an output indicates a good unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof, will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein:

FIG. 1 is an electrical diagram in block form of an MOS/LSI microcomputer chip including CPU, ROM and RAM, and utilizing features of the invention;

FIG. 2 is a memory map for the logical address space for the microcomputer of FIG. 1 and FIGS. 2a-2e are detailed memory maps like FIG. 2 for various operating modes of this microcomputer;

FIG. 3 is a greatly enlarged plan view of the semiconductor chip containing the microcomputer of FIG. 1 showing the physical layout of the various parts of the device;

FIG. 3a is an enlarged detail view of a part of the layout of FIG. 3 showing the regular pattern of the ALU and register strip;

FIG. 4 is a timing diagram showing voltage vs. time for various events in operation of the system of FIG. 1;

FIG. 5 is a detailed electrical diagram of the CPU, including ALU, shifter S, registers and busses, in the microcomputer of FIG. 1;

FIG. 6 is a detailed electrical diagram of the control ROM used in the microcomputer of FIG. 1;

FIG. 7 is a map of the relative locations of the FIGS. 7a-7f;

FIGS. 7a-7f are electrical schematic diagrams of various parts of the ALU and register strip within the CPU of the microcomputer of FIG. 1;

FIG. 7d' is a timing diagram for BCD arithmetic operations;

FIGS. 8a-8j (six sheets) show a logic flow chart of the execution of the microinstructions of Tables B and C in the microcomputer device of FIG. 1;

FIG. 9 is a map of the opcodes for the macroinstructions of Table A executed by the microcomputer of FIG. 1;

FIG. 10 is an electrical diagram, in schematic and logic form, of the entry point circuit 21 of FIG. 1;

FIG. 11 is an electrical diagram, in schematic and logic form, of the RAM 12 of FIG. 1;

FIG. 11a is a timing diagram for the RAM of FIG. 11;

FIG. 12 is an electrical diagram, in schematic and logic form, of the RAM refresh counter 31 and address multiplex circuit 32 of FIG. 1;

FIGS. 13a-13d are electrical diagrams of microprocessor systems using the microcomputer chip 10 of FIG. 1 in various operating modes;

FIG. 13e is a timing diagram for operating modes of FIGS. 13b-13d;

FIG. 14 is a block diagram of the internal peripheral circuits of the microcomputer of FIG. 1 illustrating connections to the central processing unit;

FIG. 15 is another block diagram of the circuits of the microcomputer of FIG. 1, illustrating only the interconnections between circuits;

FIG. 16a is a table illustrating the group decode circuit bus addresses which produce peripheral activating signals;

FIG. 16b is a schematic diagram of the group decode circuitry 27 in the microcomputer of FIGS. 1 or 14;

FIG. 16c is a schematic diagram of the memory control circuitry 28 of FIGS. 1 or 14;

FIG. 16d is a table illustrating the operating mode specifications for the different memory configurations of FIGS. 2 and 13;

FIGS. 17a and 17b are schematic diagrams of the interrupt circuitry 29 and I/O control register 25;

FIG. 17c is a table illustrating the interrupt vector locations in memory;

FIG. 17d is a table illustrating the input/output control register contents;

FIGS. 18a-18c are schematic diagrams of the programmable timer/event counter circuitry 26, 26a, 26b, 26c of the device of FIG. 1;

FIG. 18d is a conceptual block diagram of the programmable timer/event counter of FIGS. 18a-18c;

FIG. 18e is a table illustrating the contents of the timer data register and the timer control register;

FIG. 19a is a schematic diagram of the A port;

FIG. 19b is a schematic diagram of the B port;

FIG. 19c is a schematic diagram of the C port;

FIG. 19d is a schematic diagram of the D port;

FIG. 19e is a table illustrating interrupt generation for the system emulator mode;

FIGS. 20a and 20b are logic flow charts for a keyscan program for the system of FIG. 13a, and FIG. 20c is an electrical diagram like FIG. 13a for the program of FIGS. 20a and 20b.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT The Microcomputer Chip

With reference to FIG. 1, a microcomputer chip 10 is shown which employs features according to one embodiment of the invention. The chip 10 is a semiconductor integrated circuit of the MOS/LSI type including a silicon bar of less than about 200 mils on a side, mounted in a standard 40-pin package. Totally contained within the chip 10 is a digital processor having a ROM or read-only memory 11 for program storage and a RAM or read/write memory 12 for data storage, along with a CPU 13. The CPU consists of an arithmetic logic unit or ALU 14 with its working registers 15 and busses 16, along with a control RAM or CROM 17 for generating microinstructions or control signals on lines 18. The CPU 13 accesses the ROM and RAM memory 11, 12 by three busses: a memory data bus MD, a high address bus AH, and a low address bus AL, along with three of the control lines 18. Communication with devices external to the chip is by means of four 8-bit ports A, B, C and D which are accessed by the MD bus and operated by peripheral control circuitry as will be described. The MD, AH and AL busses are each eight bits wide, as are the ALU 14, the registers 15 and the ports, although of course concepts herein described would be applicable to 4-bit, 16-bit or 32-bit devices, for example.

The registers 15 in the CPU 13 include: an instruction register IR; a status register ST; circuitry BCD for binary-coded-decimal constants; a shift circuit S which receives the output of the ALU 14; a register T/MAH which functions as both a temporary store for operands and for the high order byte of the memory address (memory address high); a sixteen bit program counter split into two eight bit registers PCH and PCL (program counter high and low); a stack pointer SP; and a memory address low register MAL. Address buffers 19 generate true and complement address signals as busses AH' and AL' from the address busses AH and AL. Operands are for the most part stored in the RAM 12 which functions as a register file RF, rather than in temporary registers 15 associated with the CPU 13.

The busses 16 interconnect the various registers 15, the ALU 14 and MD, AH' and AL' busses. The ALU 14 always receives a P input from a P bus and an N input from an N bus, and produces an output via shifter S to an output or O bus. Access to these P, N and O busses, 16, to the registers 15 and ALU 14, and to the MD, AH and AL busses is controlled by the control signals 18 from the CROM 17.

The microcomputer chip 10 operates on the basis of 8-bit macroinstruction words stored in the ROM 11 and transferred to the instruction register IR one at a time. One example of a macroinstruction set executed in the CPU 13 is described in Table A which will be discussed in detail below. The Table gives the instruction word in mneumonics, also referred to as assembly language or source code, and also gives the machine-language opcode in binary (this is like object code except object is in hex). Usually an opcode plus one or more address bytes are used to execute an instruction. An instruction word or opcode held in IR is an input to an entry point circuit 21 which produces an 8-bit address via lines 21a to address circuitry 22 for the CROM 17, accessing one of 256 possible CROM addresses (in the example embodiment) to produce signals 18 defining a microinstruction as set forth in Tables B and C, to be described below. One macroinstruction of Table A produces a sequence of microinstructions. A part of each of the microinstructions (i.e. some of outputs 18) is used to generate the next CROM address; a microjump address is fed back to the entry point circuit via lines 23, and dispatch control information is fed back via lines 24, as will be explained. Thus, a sequence of microinstructions is generated from each macroinstruction in IR, also dependent upon status bits in the status register ST and other conditions. Addresses for operands, if needed, are contained in words from ROM 11 following the opcode and are transferred to MAL or MAH while the opcode stays in IR during this sequence.

A map of the logical address space for the microcomputer of FIG. 1 is shown in FIG. 2. The example embodiment employs 8-bit AH and AL addresses, providing a 16-bit address, and so 2¹⁶ or 65,536 bytes are available in this space (often referred to as "64K" bytes where one "K" is 1,024). The addresses are shown in four hexidecimal digits, ranging from the first address 0000 to the last FFFF. In this description memory addresses will be given in hex, unless noted. A page is 2⁸ or 256 bytes, i.e. all addresses on a page are defined by AL and the page is selected by AH. The microcomputer 10 uses the zero page (addresses 0000 to 00FF) for the register file RF in RAM 12; the "one" page (addresses 0100 to 01FF) for the peripheral file PF; and the F0 to FF pages (addresses F000 to FFFF) for the program memory of ROM 11. Some of these spaces for RF and ROM 11 may not be populated, depending upon the size of the ROM and RAM chosen. Other space such as 0200 to EFFF is available for the expansion modes as will be explained.

In the microcomputer of FIG. 1, the control circuitry responsive to the AH' and AL' buses and control bits 18 defines the way in which the CPU 13 accesses the peripheral file PF including external ports, timer, reset and interrupts, as well as memory control. An I/O and interrupt control register 25 at memory location of 0100 of FIG. 2 is loaded directly by the MD bus and is part of the ALU/register strip; this register contains two memory mode control bits which define the memory expansion modes as will be described, as well as interrupt masks and flags. A programmable timer and event counter is also included in this peripheral control circuitry, and comprises: a counter 26; a register 26a which functions as start/stop control, input select and prescaler; a control 26b; and a capture latch 26c. These elements of the timer are accessed by the MD bus and are eight bits wide, so are advantageously constructed as part of the ALU/register strip. The counter 26 is a fixed divide-by-8 pseudorandom 8-bit shift counter which simply divides is a fixed divide-by-8 psuedorandom 8-bit shift counter which simply divides its input by eight. The input to the counter 26, which may be an internal clock or an external clock or event, goes through the prescaler part of the register 26a which is an additional 5-bit divide-by-N counter loaded (via a prescale register) from the MD bus with any number up to thirty-two. The 8-bit timer register 26b is loaded from MD with the desired final count, up to eight bits or 256. When this count is reached, an interrupt INT2 is signalled. The instaneous count may be read out on MD via the 8-bit capture latch 26c without stopping an ongoing count in the counter 26; this is instigated by INT3.

In this peripheral control circuitry, a group decode circuit 27 and memory control circuit 38 receive the AH' and AL' address bits and three control signals 18 (#MEM, #WR and #MEMCNT) and produce controls which select between the ROM 11, RAM 12, ports A, B, C or D, the timer or I/O control, etc. for access by a given address. Only one of these is activated in any one cycle. The group decode 27 and memory control circuitry 28 likewise generate commands for controlling and/or selecting functions as will be explained.

Two interrupt input pins INT1 and INT3 are provided, in addition to the timer interrupt INT2. These inputs are connected to interrupt control circuitry 29 which is also responsive to the contents of the register 25. A reset input RST is used to zero or initallize the microcomputer, overriding any function or interrupt.

A mode control input pin MC connected as an input to the peripheral control circuitry provides a selection of the operating modes (along with the internally-loaded bit-7 and bit-6 of the I/O control register 25). FIGS. 2a to 2e are memory maps showing the unique parts of the address space for these modes; the register file address space RF remains the same as FIG. 2 for all modes. The modes are: (1) single-chip microcomputer mode where all memory is on-chip in the ROM 11 and RAM 12 as in FIG. 2 and the peripheral file PF is configured as in FIG. 2a, this being the primary mode of operation; (2) a peripheral expansion mode of FIG. 2b where some additional off-chip circuitry may be accessed in the PF space via ports B and C; (3) a full expansion mode of FIG. 2c where almost 64K bytes of off-chip memory may be accessed by ports B and C, the RF and ROM being the same as FIG. 2; (4) a microprocessor mode of FIG. 2d where the on-chip ROM 11 is ignored and all program memory is off-chip, but the on-chip RAM 12 is used as FIG. 2; or (5) the emulator mode of FIG. 2e in which both the peripheral file PF and the on-chip ROM 11 are disabled and all I/O and program memory is off chip, accessed by ports B and C with the on-chip RAM 12 or RF being used as in FIG. 2. The various modes allow a wide variety of different functions to be provided by one basic chip type without design, layout or microcode modifications, thus greatly reducing the cost. Input/output buffers 30 connect the ports A, B, C, D to the MD bus, as defined by direction control registers P7, P9, P11, for some mode and by the mode control arrangement via group decode 27 and memory control circuitry 28.

One of the important features of the microcomputer chip of FIG. 1 is that the RAM 12 is of the dynamic type using one-transistor cells with transparent refresh. On-chip RAM for microcomputers is usually of the static or pseudo-static type; if the RAM is of the dynamic type as in U.S. Pat. No. 4,074,351, then the refresh function may interfere with access by the CPU. In contrast, the microcomputer of FIG. 1 contains a refresh address counter 31 which is self-incrementing and may produce a new 5-bit row address to the row address decoder 12X every machine cycle, so one row of the RAM is accessed for refresh if none is accessed by the CPU. If a memory 12 access cycle is occurring, however, the counter 31 is not incremented and the refresh address output of the counter 31 is not applied to the decoder 12X. The RAM 12 is of the folded-bit-line type with a memory bit and its complement on opposite sides of sense amplifiers 12S; i.e., dual memory bits are employed instead of dummy cells traditionally used in dynamic RAMs. In the 128 byte RAM of the example, 128×8 or 1024 bits are needed, and with two one-transistor cells per bit the RAM array 12 has 2048 one-transistor cells. The array is partitioned 32×8×4, so the X decoder 12X is a one-of-32 select, the Y decoder 12Y is a one-of-4 select for each of the eight input/output bits of the RAM, and thirty-two sense amplifiers 12S are used. Of course, the RAM size can be doubled to use the whole zero page of FIG. 2, in which case 256×8×2=4096 cells are needed.

THE STRIP ARCHITECTURE

In FIG. 3, the microcomputer of FIG. 1 is illustrated in chip layout form. A major part of the area of the chip 10 is occupied by the memory including the ROM 11 and RAM 12 with their address decoders. The ROM 11 has associated with it an X address decoder 11X and a Y address decode and ROM data output circuit 11y of conventional design; eleven address bits are used to define one of 2048 eight-bit bytes in the ROM (twelve bits if a 4096 byte ROM is employed), so an address for the ROM needs both the MAL and MAH registers, i.e., address bits from both AL and AH buses. The RAM has an X address decoder 12X which selects 1-of-32 row lines, and a Y address decoder 12Y which selects 1-of-4 column lines, so only seven bits are needed for the RAM select (eight if a 256 byte RAM is used). Another major part of the chip area is the control ROM 17 and its associated X and Y decoders 22X and 22Y, and output buffers 17b. If fully populated, the number of bits in the control ROM would be 256 times the number of output lines 18. Only forty-five output lines 18 are needed for the example instruction set of Table A, and only 160 microinstruction addresses as in Tables B and C, so the control ROM is only 160×45 or 7,200 bits. The output ports A, B, C, and D each have eight bonding pads on the chip (total of thirty-two) for connection to external, and the areas of the chip around these bonding pads are occupied by the buffers 30 used for the ports. It will be noted that the port A is only used for input, so the space needed for the input buffers for this port is much less than for the remaining ports B, C, and D which require tri-state output buffers.

Between the ROM 11 and the CROM buffers 17b on the chip 10 of FIG. 3 is the "strip" which is an array of rows (parallel to control lines 18) and columns (parallel with metal bus lines 16 and register/ALU bits 14, 15) containing all of the 8-bit registers, ALU bits, and like circuitry associated with the busses 16 and control lines 18. As set forth in prior application Ser. No. 210,109, filed Nov. 24, 1980 by McDonough, Guttag and Laws, assigned to Texas Instruments, now U.S. Pat. No. 4,402,044, an important feature is that the ALU 14 and its associated registers IR, ST, S, T/MAH, PCH, PCL, SP, and MAL as described above are laid out on the MOS/LSI chip 10 in a regular strip pattern as seen in FIG. 3. Other circuitry connected to the busses and having controls 18 shared by eight bits is also in the strip, such as entry point 21, address buffers 19, timer 26, I/O control register 25, etc. Each of these registers as well as the ALU contains eight bits or stages which are laid out in a pattern like memory cells, the bits arranged horizontally and alligned vertically as seen in FIG. 3. The MD, AL, AH, O, N and P busses of FIG. 1 are each eight parallel metal strips on top of the cells of the ALU and registers (rather than besides the registers as depicted in FIG. 1), and all of the dozens of control lines 18 are horizontal polysilicon lines typically used as the control gates for transistors in the ALU 14 and its registers and like circuitry. The number of control lines 18 needed for the ALU 14 is greater than for a single register such as the MAL register, for example, and conveniently the space needed to lay out the ALU stages is greater than for a single register, so waste space is minimized. That is, the space needed in the control ROM 17 to generate the controls 18 is about the same as the space needed for the controlled circuitry. This layout arrangement is indeed advantageous because the ALU and registers fit alongside the control ROM with virtually none of the wasted space used merely for routing conductors in conventional construction of microprocessors. All bus lines MD, AL, AH, O, N and P, and all control lines 18 are routed over functional regions or cells of the chip rather than over unused silicon, and almost all 90 degree turns are produced inherently at functional cells rather than in conductor routing. In the prior devices, the control ROM, the registers, the ALU, etc., were islands of circuitry connected by busses or conductors. The enlarged view of FIG. 3a shows a small part of the strip, two-bits wide, illustrating the metal bus lines and the polysilicon control lines 18 for an N-channel silicone gate MOS device made generally by a single-level polysilicon process according to U.S. Pat. No. 4,055,444, assigned to Texas Instruments. Various contacts (not shown) would be made within each register bit or stage from metal to silicon or to polysilicon. It is significant to note that most of the connecting lines from registers to busses illustrated in FIG. 1 are not physically lines or elongated conductors at all but instead are merely metal-to-silieon or metal-to-poly contact areas along the metal bus lines of FIG. 3a. That is, routing of 8-bit sets of parallel conductors is minimized by the strip feature, and the size of the chip 10 is reduced. The busses 16 are staggered so that all six busses are not needed in any one art of the strip, and thus the pitch or maximum width of cells of the strip is minimized since the metal-to-metal spacing is a critical limiting factor in bit density. To this end, the placement of the registers 15 are such that the N bus need not co-exist in any register with the AL or AH busses, and the P bus ends where the AL bus starts, as illustrated in FIGS. 1 and 3a. Some of the clocks needed in the registers and ALU of the strip are run in metal lines like the busses 16 (H1,H4 shared in FIG. 3a) so these place further constraints on the density and make the strip concept and bus/register optimum placement more significant. Connections from MD to P or N busses are made by transistors located in the strip like a register and labelled MDtP, MDtN; since this logic requires eight parallel bits of transfer gates, tied to sets of eight parallel busses, and using CROM outputs 18 as controls, it fits well in the strip.

The control ROM 17 my be of the "compressed" design as set forth in U.S. patent application Ser. No. 209,915, filed Nov. 24, 1980, by Guttag, McDonough and Laws, now U.S. Pat. No. 4,402,043, although as described herein the CROM is on non-compressed design. The CROM fits alongside the strip to provide the controls 18 in the control-intensive areas of the ALU and register/bus connections, and alongside the entry point circuit 21 where the address control and jump address lines 23, 24 are needed. The design is oriented toward the control ROM as the source of all controls rather than random logic, and the chip layout of FIGS. 3 and 3a illustrates that the area of the chip is dominated by the ROM, RAM and CROM with their decoders, and the strip containing a regular array of ALU/register bits, with little space occupied by other control logic. This design approach is enhanced by and enhances the microprogramming facility which makes the microcomputer 10 particularly easy to modify by changing the micro or macrocode.

The microcomputer 10 may be modified at three levels, plus the mode control. The first level is changing the ROM code of the ROM 11, and of course this is the most widely practiced modification. The ROM code is defined by a single mask in the manufacturing process as set forth for example in U.S. Pat. Nos. 3,541,543, 4,208,726 or 4,230,504, assigned to Texas Instruments. The macroinstruction set may be supplemented (keeping basically the same microinstruction set), or the microinstruction set may be changed, both of these levels requiring changes in the CROM 17 code upon manufacture. The CROM code is defined by a single mask in manufacture, just as the ROM code, so physically it is just as easy to change the microinstruction set; however, the macro assemblers and micro assemblers (computer programs used as design aids for customers) then are different. In addition to these ways of altering the device 10, the sizes of the ROM and RAM may be increased to allow more complex algorithms to be programmed in the ROM code, and the size of the CROM 17 may be increased to provide more complex micro- and/or macro-instruction sets. It is important to note that the mode control MC (and bits 6-7 of register 25) allows changes without any type of physical or mask change; no fuse links or the like are needed.

System Timing

The microcomputer chip 10 operates from a basic clock frequency referred to as Xtal in FIG. 4. This frequency of about 5 MHz is supplied by an internal oscillator 33 controlled by an external crystal coupled to two pads labelled Xtal in FIG. 1 or 3. From the clock Xtal, clock generator circuitry 33 produces four basic overlapping half-cycle clocks H1, H2, H3 and H4 for each microinstruction cycle or state time S1, S2, etc., as seen in FIG. 4. Each state time equals two complete cycles of the clock Xtal. H4 overlaps two state times.

Short memory cycles to access the RAM 12 are completed in one state time such as S1 of FIG. 4; #MEMCNT is low and all bits of the AH bus are low during H1, and the RAM address is valid on the AL bus while #MEM is high. The write control #WR is high for write or low for read. The data accessed is then valid on the MD bus during H4 at the end of the cycle, extending over into the beginning of the next cycle, so the data may be loaded into the registers T or IR at the end of a cycle or gated onto the P or N busses at the beginning of the next cycle.

All memory references to the register file RF in the RAM 12 use this short cycle; all other memory references (i.e. to the on-chip ROM 11, the peripheral file PF, and extended memory) require two microinstruction executions and are called long memory cycles as illustrated in FIG. 4. For long cycles, the memory continue command #MEMCNT is high during the first state time and low during the second. The memory command #MEM must be high during H1 of both cycles, and the address valid on AH and AL during H1 of the first cycle. For read, the write command #WR is low from the beginning of the first cycle through H1 of the second, and the data is valid during H4 beginning at the end of the second cycle. For long write, #WR is high, and the write data is gated onto the MD bus for H4 of both first and second cycles.

Within a given state time or microinstruction cycle, the address on the AH' and AL' busses becomes valid during H2. This address is based on the address loaded onto AH and AL during H1. In the ROM 11, the array is precharged during H1 with all row or X lines going to VSS and all column or Y lines going to Vcc, then the ROM X address gated into the array from decoder 11X beginning at H3 and the ROM Y address coming valid at the beginning of H4, so the ROM output is valid at H4.

The CPU

The CPU 13 in the microcomputer 10 of FIG. 1 consists of the ALU 14, the registers 15 and the busses 16 controlled by the CROM 17. In FIG. 5 a more detailed block diagram of the ALU and shifter S and the associated busses is shown, and FIG. 6 shows the CROM 17 and its microinstruction output bits 18. Control of the ALU and access to the busses is defined entirely by these microinstructions or bits 18, identified in FIG. 6 for the illustrative embodiment. An 8-bit address on lines 21a from the entry point circuitry 21 contains a 6-bit X address on lines 21X and a 2-bit Y address on lines 21Y. The lines 21X are connected to X decoder 22X which selects one of up to 64 X lines in the array of ROM bits of the CROM 17. The lines 21Y are connected to a Y decoder 22Y which selects 1-of-4 in each group of four Y lines (only forty-five groups used). Thus, for each 8-bit address on lines 21a, a different "microinstruction" is output on the lines 18; a microinstruction may have any number of the lines 18 active, but usually a combination of only a few lines 18 is active for a given microinstruction. Each line 18 goes to a buffer 17b to drive a higher capacitance load than the array output Y line itself would allow, and to clocked gates and other such logic as needed. All microinstruction bits (control lines 18) in FIG. 6 and throughout this description are referred to with a prefix "#". Some bits are active low and thus have a minus sign, like #-OtST. In the microinstruction bits of FIG. 6, the letter "t" means "to", so #-OtST means "O bus to ST register", i.e., the gates connecting th O bus to the status register are activated by this bit. The eight bit jump address on the lines 23 is denoted #JmpAddr (7-0), while the 3-bit jump control on the lines 24 used for dispatch addressing is denoted #JmpCntl (2-0); these eleven bits are used in the entry circuit 21 to generate the next CROM address. All of the twenty-one bits 18 from #OtPCH down to #ONEtAH in FIG. 6 control the access to registers 15 from busses 16. Of these, #LowWrite0 and #LowWrite 1 are decoded to produce pseudo-microinstructions OtPCL, OtMAL and OtSP. The bits #ONEtAL and #ONEtAH place a "1" on the AL or AH busses to generate the B register address 0001 or the PF page address 0100 (hex) in a microinstruction. Default to all 0's on AL and AH is A register address in the register file. Connections between registers 15 and busses 16 are described in detail below. The #MEMCNT bit is a "memory continue" control for long memory cycles; the RAM 12 can be accessed for read or write in one state time, but the ROM 11 or peripherals in PF require two states, so for this reason control line #MEMCNT is active in the first state of every long memory cycle as seen in FIG. 4. #MEMCNT is used to form several other control signals, and always identifies the first or second state of a long memory cycle. The #MEM bit signifies a memory cycle and is active whenever ROM 11, RAM 12 or external memory is accessed. The #WR bit is a write command, so if #MEM and #WR are active a memory write condition exists, while if #MEM is active and #WR is not, a memory read condition exists. The #-List signal is a load status command for ALU operations; the status register ST can also be loaded from the O bus by the #-LST command. The ALU is controlled by nine bits labelled #ShiftCntl (3-0), #AluCntl (3-0) and #ABL; these controls will be described below in detail.

The microinstruction bits 18 are physically arranged in the order used in FIGS. 7a-7e rather than in the order shown in FIG. 6, so that a control bit 18 is generated as close as possible to the point it is used in the strip.

The microinstruction control of access to the registers 15, busses 16 and ALU 14 will now be described in reference to FIGS. 5, 6 and 7a-7f.

P Bus

The P bus is one of the inputs to the ALU 14. It is called `P` for "Positive", because in a subtract operation where the ALU 14 only computes P-N the P bus contains the positive, or left-hand, operand. The P bus is loaded from the MD bus via transistors 16a, 16b, and 16c, loaded from the AL bus via transistor 16d (FIG. 7b), loaded from the PCH register via transistor 16e, or from the PCL register via transistor 16f. Any of the AL bus sources may be placed on the P bus by gating them on the AL bus and asserting the #PAL microinstruction bit going to the gate of transistor 16d, connecting the P bus to the AL bus. If no source is specified, i.e., "default", the P bus assumes the value of all zeros. The P bus is loaded in the beginning of a microinstruction cycle, on phase H1. All of the possible P bus sources and the microinstruction bits or outputs 18 needed for each are as follows:

    ______________________________________                                         P Bus              Microinstruction                                            Source             Bit(s)                                                      ______________________________________                                         MD Bus             #MDtP                                                       PCH Register       #PCHtP                                                      PCL Register       #PCLtP                                                      MAL Register       #MALtAL,#PAL                                                SP Register        #SPtAL,#PAL                                                 01 Constant        #ONEtAL,#PAL                                                ______________________________________                                    

N Bus

The N bus is the other input to the ALU 14. It is called N for "negative", since on the ALU subtract operation it contains the negative, or right-hand, operand. It is loaded from the MD bus via transistors 16a, 16g and 16h, loaded from the T/MAH register via transistor 16i, loaded from the IR register via transistor 16j, the status register ST via transistor 16k, or the BCD constant register via transistor 16m. It is understood, of course, that there are sets of eight of each of the transistors 16a to 16j, one for each of the eight bits of each bus and each register. Only four transistors in the sets 16k or 16m are needed. The source of the N bus is indicated directly by a bit in the microinstruction word, as shown below. If the bits is `1`, the source is gated onto the N bus. If no source is specified, the N bus assumes the value of all zeros. The N bus is also loaded at the beginning of a microinstruction cycle, on phase H1.

    ______________________________________                                         N Bus              Microinstruction                                            Source             Bit(s)                                                      ______________________________________                                         MD Bus             #MDtN                                                       T Register         #TtN                                                        Status Register    #STtN                                                       BCD Constant       #BCDtN                                                      IR Register        #IRtN                                                       ______________________________________                                    

AL Bus

The AL or address low bus holds the lower eight bits of all memory addresses. This comprises the entire address for references to the register file RF in RAM 12, or the lower byte for references to the peripheral file PF, on-chip ROM 11 and extended memory in expansion modes. The AL bus is loaded during the phase H1. The sources of the AL bus are the MAL register via transistor 16n, the SP register via transistor 16p, or the constant 01 via transistor 16q. The constant is provided to efficiently address RAM location 01 which is the "B" register. If no source is specified, "default", the AL bus assumes the value 00 which is the A register in the RAM.

The AL bus may also be connected to the P bus via transistor 16d by asserting the #PAL microinstruction bit. In this manner, the AL bus sources (MAL, SP, and the constant 01) may be gated onto the AL bus and then onto the P bus to be operated on by the ALU. Likewise, the P bus sources (PCH, PCL, and MD bus contents) may be gated onto the P bus and then onto the AL bus via transistor 16d and #PAL to serve as low order address lines. The MD bus contents moved in this case are those present at the start of the microinstruction. In summary, all of the possible sources of the AL bus are listed below:

    ______________________________________                                         AL Bus             Microinstruction                                            Source             Bit(s)                                                      ______________________________________                                         MAL Register       #MALtAL                                                     SP Register        #SPtAL                                                      PCL Register       #PCLtP,#PAL                                                 PCH Register       #PCHtP,#PAL                                                 MD Bus             #MDtP,#PAL                                                  01 Constant        #ONEtAL                                                     ______________________________________                                    

AH Bus

The 8-bit AH (Address High) bus contains the high-order byte of the address referenced by the CPU, loaded during H1. It may be loaded with the contents of the PCH register via transistor 16r, the T/MAH register via transistor 16s, or the constant 01 via transistor 16t. The high byte of the program counter is usually transferred to the buffers 19 for use in the peripheral control circuitry 20, and the T/MAH register is used to hold the high byte of other addresses in memory for use in a later microinstruction state. The constant 01 is provided to efficiently access addresses in the peripheral file in this embodiment (i.e. page-one addresses of the form 01xx in hex). If no source is explicitly specified in the microinstruction word, "default", the AH bus takes on the value 00; this is useful for referencing the on-chip register file RF in RAM 12. The sources of the AH bus are summarized below:

    ______________________________________                                         AH Bus              Microinstruction                                           Source              Bit(s)                                                     ______________________________________                                         PCH Register        #PCHtAH                                                    T/MAH Register      #TtAH                                                      01 Constant         #ONEtAH                                                    ______________________________________                                    

O Bus

The O or output bus always contains the output of the ALU 14 and shifter S combination. As seen in FIGS. 5 and 7c, the O bus contents may be loaded onto the MD bus via transistors 16u and OtM, or into the PCH, PCL, MAL, or SP registers via sets of eight each of transistors 15a to 15d, respectively. The status register ST is loaded from O bus by the true-low microinstruction bit #-OtST and four transistors 15e (FIG. 7e). The PCH register is loaded by the true-high microinstruction bit #OtPCH. The load signals for the other destination registers (MAL, PCL, SP) are encoded in the two microinstruction bits #LowWrite(1-0), according to the combinations of #LowWrite(1-0) below:

    ______________________________________                                         #LowWrite        O Bus        Pseudo-                                          (1)    (0)       Destination  Microinstruction Bit                             ______________________________________                                         0      0         No Write                                                      0      1         MAL Register OtMAL                                            1      0         PCL Register OtPAL                                            1      1         SP Register  OtSP                                             ______________________________________                                    

There is no microinstruction bit that directly loads the MD bus from the O bus, because the MD bus contents are under control of the peripheral control circuitry 20. This transfer is controlled by the OtM signal sent from the circuitry 20 to the CPU on a control line. OtM is asserted on every memory write cycle (on-chip or extended memory), and on the first state of every long memory cycle.

The O bus may be gated onto the MD bus via transistors 16u by specifying the appropriate values of the #MEMCNT and #WR microinstruction bits so that OtM will be asserted by the peripheral control circuitry 20. The O bus contents may then be loaded into the T/MAH or IR register from the MD bus via transistors 15f and 15g.

In summary, the destinations of the O bus are described below:

    ______________________________________                                         0 Bus            Microinstruction                                              Destination      Bit(s)                                                        ______________________________________                                         ST Register      #-OtST                                                        PCH Register     #OtPCH                                                        PCL Register     OtPCL                                                         MAL Register     OtMAL                                                         SP Register      OtSP                                                          T Register       #WR,#MDtT                                                     IR Register      #WR,#MDtIR                                                    Short Mem Cycle  #WR,#MEM                                                      Long Mem, Cycle 1                                                                               #MEMCNT,#WR,#MEM                                              Long Mem, Cycle 2                                                                               #WR,#MEM                                                      ______________________________________                                    

The O bus is loaded during phase H4 of the microinstruction cycle. It contains the result of the ALU and shifters operations specified in the current microinstruction. The OtM function is summarized in Table H.

MD Bus

The memory data bus MD is a bidirectional bus that transfers data to and from the CPU 13. Data is valid on MD during phase H4 of the microinstruction cycle, which spans two microinstructions. For example, data may be read via transistors 16b from the MD bus onto the P bus at the beginning of a cycle H1 and the ALU results then loaded back onto MD via transistors 16u at the end of the cycle H4. As indicated above, Table H sets forth this OtM function and the memory controls.

At the beginning of a cycle, the MD bus contents may be loaded on the P or N busses via transistors 16c or 16h, as described earlier (FIG. 5 or 7b). Thus the results of the previous microinstruction (or the data red from memory by it), may be loaded into the ALU 14.

At the end of a cycle, the MD bus may be loaded in one of three ways;

(1) The O bus contents may be gated into the MD bus via transistors 16u and OtM;

(2) The on-chip RAM 12 or ROM 11 may place data onto the MD bus; or

(3) The peripheral control circuitry 20 may place data onto the MD bus from ports A, B, C or D, latch 26c, I/O control register 25, etc.

The MD bus contents are controlled by the peripheral control circuitry which sends the OtM signal to the CPU to signal loading the bus from the O bus. The CPU 13 requests use of the MD bus by asserting combinations of the #MEM, #MEMCNT, and #WR signals, as outlined above. The group decode and memory control 27, 28 in the peripheral control circuitry 20 sends signals to the on-chip ROM 11 and RAM 12 to control their accesses to the MD bus.

The timing of read and write accesses to memory is explained with reference to FIG. 4. For short memory reads, the data on MD bus is available at the end of the same microinstruction cycle that initiated the read. Data on MD may be loaded into the T/MAH or IR registers during that microinstruction by specifying the #MDtT or #-MDtIR bits, respectively, or may be loaded into the P or N bus on the next microinstruction by specifying the #MDtP or #MDtN bits in the next microinstruction. For short memory cycle writes, the O buts data is placed on the MD bus, and the #WR control asserted. For long memory reads, the desired address is placed on the AH and AL lines, and the #MEMCNT command asserted in the first of the two cycles required. At the end of the second cycle, the data is available on the MD bus. (By a command "Load Address", LDADDR, the memory address is latched in buffers 19 going to AL' and AH' and the peripheral control circuitry 20 on the first cycle, and need not be asserted on the second cycle). For long memory writes, the address is specified in the first cycle, and the data is placed on the MD bus for the first and second cycles.

In summary, the destinations of the MD bus in the CPU 13 are described below:

    ______________________________________                                         MD Bus                     Microinstruction                                    Destination   When Loaded  Bit(s)                                              ______________________________________                                         T/MAH Register                                                                               End of Cycle #MDtT                                               IR Register   End of Cycle #-MDtIR                                             P Bus         Start of Cycle                                                                              #MDtP                                               N Bus         Start of Cycle                                                                              #MDtN                                               ______________________________________                                    

The MD, P, N, AH, AL and O busses are precharged on H2 or H3 by transistors 16v as indicated.

ALU Operation

The arithmetic logic unit or ALU 14 as seen in block form in FIG. 5 and in detail in FIGS. 7c and 7c' accepts as inputs the values on the P bus via transistors 14a and N bus via transistors 14b. The ALU outputs its result to the shifter S during H4 via line 14c and transistor 14d. Its operation is controlled by the #AluCntl(3-0) bits inputted via buffers 17b and transistors 14e, and by the #ABL bit going to transistors 14f, both from the current microinstruction. The ALU operates on the values loaded on the P and N busses during H1 of the current microinstruction, and produces an 8-bit ALU output on lines 14c which is input to the shifter S, and also produces two carry bits: Cout on line 14g, an arithmetic full byte carry bit, and Dout on line 14h, a 4th-bit half-carry bit used by the decimal adjust circuitry in the BCD constant register for binary coded decimal operations. The available operations of the ALU controlled by transistors 14e and 14f are defined below:

    ______________________________________                                         #AluCntl          ALU Output                                                   3   2     1     0   #ABL  on Lines 14c Operations                              ______________________________________                                         0   0     0     0   0     P + N + Cin  Add                                     0   0     0     0   1     P XNOR N     Exclusive NOR                           0   0     0     1   1     P AND N      AND                                     0   0     1     0   1     (NOT P) OR N OR                                      0   0     1     1   1     N            Pass N                                  0   1     0     0   1     P OR (NOT N) OR                                      0   1     0     1   1     P            Pass P                                  0   1     1     0   1     FF(hex)      all 1's                                 0   1     1     1   1     P OR N       OR                                      1   0     0     0   1     P NOR N      NOR                                     1   0     0     1   1     OO           All 0's                                 1   0     1     0   1     NOT P        Invert P                                1   0     1     1   1     (NOT P) AND N                                                                               AND                                     1   1     0     0   1     NOT N        Invert N                                1   1     0     1   1     P AND (NOT N)                                                                               AND                                     1   1     1     0   1     P NAND N     NAND                                    1   1     1     1   0     P - N - 1 +  Cin                                                                            Subtract                                1   1     1     1   1     P XOR N      Exclusive OR                            ______________________________________                                    

The carry-in bit Cin on line 14i of the ALU 14 is specified by the #ShiftCntl(3-0) bits 18 of the microinstruction. For operations requiring no shifting of the ALU contents, #ShiftCntl(3,2) bits are zero and the possible carry-in bits are defined in logic 14j of FIG. 7c' as follows:

    ______________________________________                                         #ShiftCntl              ALU Carry In                                           3     2         1     0       on Line 14i                                      ______________________________________                                         0     0         0     0       0                                                0     0         0     1       1                                                0     0         1     0       uC; micro carry bit                              0     0         1     1       STC; status carry bit                            ______________________________________                                    

The micro carry bit uC is the carry out Cout on line 14g from the ALU operation of the immediately preceding microinstruction. This is not the same as the shift-out bit Sout on line 14k from the shifter S operation of the previous microinstruction. The status carry bit STC is the carry bit of the status register ST.

The first section of each ALU bit produces a "generate" on line 14m and/or a "propagate" on line 14n. The arithmetic carry-out Cout bit from the ALU 14 on line 14g is generated and/or propagated by transistors 14f, 14p and 14q, depending upon #ABL, and if `1` is there is a carry-out during an add or subtract operation in the ALU. For the add operation, Cout=1 indicates there was a carry, i.e. the sum of the (unsigned) operands exceed 2⁸. For the subtract operation, Cout=0 indicates there was a borrow, i.e., the P operand was lower than the N operand (unsigned). For all other operations (i.e. logical operations), Cout on line 14g is equal to 0. Cout is sent via line 14g to the status register ST circuitry for possible loading into STC, the status carry bit. The decimal half-carry Dout is sent via line 14h to the BCD constant register for use in generating a constant for decimal arithmetic correction. In each bit of the ALU, the propagate bit on line 14n and a carry-dependent bit 14p' are inputs to an exclusive-or circuit 14r, which produces the output 14c.

As an example of ALU operation, an add operation with zero carry in (#AluCntl and #ShiftCntl all zeros) will cause the ALU to calculate the sum of the P and N bus contents. To calculate the difference between the P and N bus contents, #AluCntl=1111 and #ShiftCntl=0001. A `1` must be carried in for this subtract since no borrow was desired. As a complete example, the following two microinstructions read the current byte addressed by the PCL and PCH registers, place it in the T/MAH register, and increment the PCL and PCH registers:

    ______________________________________                                         Bits(s)        Operations(s)                                                   ______________________________________                                         FIRST                                                                          MICROINSTRUCTION                                                               CYCLE:                                                                         #PCLtP,#PAL    Place PCL on AL bus via P bus                                   #CPHtAH        Place PCH on AH bus                                             none (default) Place all zeros on N bus                                        #AluCntl = 0000,                                                                              Adds P and N with Carry in (sets                                #ShiftCntl = 0001                                                                             micro carry uC) to increment PCL                                               by 1                                                            #LowWrite = 10 ALU output goes back to PCL with                                (OtPCL)        no shift, via O bus                                             #MEMCNT,#MEM   1st cycle of long read                                          #Jump Addr XXXXXXX                                                                            Go to this CROM address for second                              #Jump Cntl XXXX                                                                               microinstruction cycle                                          SECOND                                                                         MICROINSTRUCTION                                                               CYCLE:                                                                         none (don't care-AH,AH)                                                                       The contents of AH and AL busses                                               were latched in buffers 19 on                                                  the first cycle                                                 #PCHtP         Place contents of PCH register on                                              P bus                                                           none (default) for N                                                                          Place all zeros on N bus                                        #AluCntl = 0000,                                                                              Add the micro carry uC from the                                 #ShiftCntl = 0010                                                                             PCL increment in first cycle                                    #OtPCH         ALU output via O bus (no shift) is                                             placed back in PCH register                                     #MEM           Memory read continues                                           #MDtT          Place the byte read into the T/MAH                                             register via MD bus                                             #Jump Addr XXXXXXX                                                                            Go to next instruction                                          #Jump Cntl XXXX                                                                ______________________________________                                    

Notice that an increment was done in the first cycle by using an ALU carry-in of `1`. The second instruction incremented the high byte of the program counter in PCH only if the micro carry bit (uC) generated in the first cycle was `1`.

Shifter Operation

The shifter S of FIGS. 5 and 7 performs a variety of 1-bit shift operations on the outputs 14c of the ALU 14. The #ShiftCntl(3-0) bits on control lines 18 to the ALU control the following entities:

(1) the ALU carry in bit Cin via logic 14j and input line 14i;

(2) the shift direction left or right via transistors Sa or Sb, left and right control lines Sc and Sd (or straight on Si), and logic Se; and

(3) the bit shifted in via line Sf and Sg.

The following describes the various combinations of shift control lines:

    ______________________________________                                         #ShiftCntl    ALU        Shift     Shift-In                                    3     2     1       0   Carry In Direction                                                                              Bit                                   ______________________________________                                         0     0     0       0   0        No      --                                    0     0     0       1   1        Shift   --                                    0     0     1       0   uC               --                                    0     0     1       1   STC                                                    0     1     0       0   1        Shift   ALU(7)                                0     1     0       1   0        Left    ALU(7)                                0     1     1       0   1                STC                                   0     1     1       1   0                STC                                   1     0     0       0   1        Shift   ALU(0)                                1     0     0       1   0        Right   ALU(0)                                1     0     1       0   1                STC                                   1     0     1       1   0                STC                                   1     1     x       x   x        Invalid --                                    ______________________________________                                    

For #ShiftCntl=00xx, no shifting is performed and the transistors Sh are turned on by Si and logic Sj, so the ALU outputs bits go to transsitors Sk as inputs to the 0 bus; the ALU carry-in bit 14i is as described in the ALU description, above. For #ShiftCntl=010X, the ALU output is rotated left via transistors Sa, with the least significant bit, ALU(1), shifted in via line Sf. For #SchiftCntl=011x, the ALU output is rotated left through the status carry bit, STC, via lines Sm and 14k. For #ShiftCntl=100x, the ALU output is rotated right via transistors Sb, and for #ShiftCntl=101x, the output is rotated right through the status carry bit in ST via lines Sn, Sp, Sq and logic Sr. In each case, #ShiftCntl(1) indicated the SLU carry-in bit.

The shift-out bit Sout on line 14k shifted out in a rotate instruction is sent to the status register ST. It will be loaded in ST as the new status carry bit STC if the #-LST microinstruction bit is set.

IR Register

Referring to FIGS. 5 and 7a, the 8-bit instruction register IR is a register intended to hold the current machine opcode (one of the opcodes or first bytes of the Table A instructions). The opcode is loaded through transisors 15g from the MD bus by the #-MDtIR bit in a microinstruction. IR may be loaded onto the N bus with the #IRtN bit through transistors 16j.

The output of IR, includes true outputs IR0 to IR7 and complement outputs -IR0 to -IR7, all on lines 21b; this output primarily is used in the entry point circuit 21 as will be described.

Each of the bits of the registers 15 of FIG. 7 basically consists of two inverters 15i with the output coupled back to the input via a transistor 15j. All transistors 15j are clocked on H2 except for IR and ST in which the transistor is clocked on H1.

Status Register

The status register ST of FIGS. 5 or 7e is a 4-bit register indicating various conditions of the machine. Each bit of the status register has a special meaning, and has separate circuitry devoted to it. Only bits 4-7 of ST are used in this example, but other embodiments could use additional bits.

STC or the "C" bit referred to in instructions of Table A is the status carry bit. It holds either the carry-out of the ALU 14 from line 14g, the shift-out of the shifter S from line 14k, or the decimal arithmetic carry-out from line 14h. STSB is the status sign bit ("N" in Table A), and contains the most significant bit of the O bus contents. STEZ is the status equal to zero bit, and contains a `1` when all bits of the O bus are zero which is detected by transistors Sz and line Sz2 in shifter S. STINT is the status interrupt enable bit. Bits 3-0 of the status register are not used in this embodiment but may be used in expanded versions of the device; the value of these bits whern the ST register is loaded onto the N bus is undefined.

The status register bits may be modified in one of two ways:

(1) by asserting #-OtST, all bits may be replaced by the contents of the O bus via transistors 15e; or

(2) by asserting #-LST the STC, STSB, and STEZ bits may be set according to their particular input circuitry via transistors 15n (the STINT bit is unaffected in this case).

There is no way to individually load the STC, STSB and STEZ bits; they are loaded together via transistors 15n and #-LST. This feature permits an efficient implementation of the status logic, typically a very costly item (in space used) in single-chip microarchitectures. The special circuitry defining the value of the STC, STSB, and STEZ register bits is described in the following paragraphs.

When the #-LST signal is asserted, the STC bit will be loaded from one of three sources:

(1) from the ALU arithmetic carry-out Cout on line 14g, via transistors 15p and 15n. Cout is the carry/borrow bit generated by the ALU on arithmetic operations. Cout is loaded if no shifter S operation is specified, i.e. #Shift Cntl=00xx.

(2) from the shifter S shift-out bit Sout on line 14k, via transistor 15n. This is the bit shifted out on shifter operations. If a shifter operation is specified (i.e. #ShiftCntrl other than 00xx), then Sout is loaded into the carry bit.

(3) from a BCD decimal carry/borrow-out bit on line 15q and transistor 15r. This is the carry bit computed by the decimal adjust circuitry within the BCD constant register. It is loaded into the STC status carry bit if the #BCDtN bit is set, indicating a decimal adjust constant is loaded onto the N bus.

When the #BCDtN microinstruction bit is present, indicating a decimal adjust operation, no shift should be applied to the ALU output.

When #-LST is asserted, the input to the STSB bit is bit-7 of the O bus, the most significant bit of the O bus, via transistor 15n.

When #-LST is asserted, the input to the status equal to zero STEZ bit is the micro equal-to-zero bit, uEZ from the shifter S, derived from the transistors Sz. The uEZ bit is simply the logical NOR of all O bus lines. That is, if all O bus line are zero, the uEZ is set to `1`. Otherwise, it is set to `0`.

The status interrupt enable STINT bit may only be modified by loading the O bus contents into the status register ST via transistor 15e when #OtST is asserted. The STINT bit corresponds to bit-4 of the O bus in this case. STINT is output from the CPU 13 to the peripheral control circuitry 20 on a control line from the CPU. If STNT=0, the circuitry 20 will not pass on an interrupt to the CPU via the IACT control line. If STINT=1, the IACT control is asserted by circuitry 20 on an interrupt. By dispatching on the IACT bit, the microcode is able to test for interrupts.

All of the status bits may be loaded from the status register ST to the N bus via transistors 16k. The STEZ, STSB and STC bits go to the entry point circuit 21 via lines 21b.

Microinstruction Sequence Control With Dispatching

The micro architecture of the invention including entry point circuit 21 and CROM 17is designed to dispatch on various subfields of the IR contents, providing for the execution of appropriate microcode as in FIG. 8 and Table B and C for each machine opcode or Table A instruction. FIG. 9 shows a map of the opcodes. The opcode in IR may be considered to have two possible formats, and the entry point circuit 21 seen in detail in FIG. 10 responds to these formats to produce the address on line 21a:

Format 0 is indicated by a 10` in IR(7), the most significant bit of the IR register (all opcodes with 0000 to 0111 for their most significant half). In this format, bits IR(6-4) form a 3-bit "group" field via transitors 21g and bits IR(3-0) form a 4-bit "function" field via transistors 21f. These are the basic arithmetic and logic dual-operand instructions, for the most part.

Format 1 is indicated by a `1` in IR(7) (all opcodes with 1000 to 1111 for MSH). In this format, bits IR(6-3) form a 4-bit "group" field via transistors 21g' and bits IR(2-0) form a 3-bit "function" field via transistors 21f'. These include the peripheral page instructions, single operand instructions, special addressing (direct, indirect, indexed) and traps.

The terms "group" and "function" refer to logical subsets of machine opcodes. In the example shown, the group field in an opcode indicates the addressing mode of the instruction (i.e. which group of FIGS. 8b to 8d to go to on the first dispatch at decision point 8m), and the function field indicates the arithmetic or logical opration performed on the operands on the second dispatch at points 8n of FIGS. 8b to 8d, after the operands are fetched. The microarchitecture allows significant sharing of microinstructions among opcodes within the same group or function. In the microcode for the illustrated embodiment, for instance, all opcodes of the format 1 share a microcode state RftoA-1 which fetches the A register and a general RF register, as seen in FIG. 8 and as will be explained in reference to Tables B and C.

The mechanisms for dispatching on the group and function field values in the IR are described herein. Dispatching on an IR subfield may be performed on one of the first microinstruction after the IR is loaded (e.g., at IAQ-2). Thereafter, dispatching may be performed by microinstructions up to and including the next one that reloads the IR. If no dispatching is required during executing a given opcode, then the IR may be used as a general purpose 8-bit register.

The flow of control between microinstructions is determined by how the next microinstruction address on lines 21a to CROM 17 is generated in the circuit of FIG. 10, in both conditional and unconditional branching. The dispatching capability of the processor is used to share microintructions among several macroinstructions.

The microinstructions of Tables B and C, stored in the control ROM or CROM 17 on the chip, may be characterized as horizontally microprogrammed in that each microinstructon indicates the address at which the next microinstruction to be executed is located. The next micro-address is specified by two fields of the CROM output 18 (lines 23 and 24) indicated as inputs in the logic circuit of FIG. 10;

(1) #JumpAddr(7-0), an 8-bit field indicating a base address in CROM; and

(2) #JmpCntl(2-0), a 3-bit code indicating one of eight dispatch offsets from the base address in #JmpAddr(7-0); also complements of #JmpCntl, such as -Jmp(Cnt(12), are used.

If 190 JmpCntl(2-0)=`000`, then the #JmpAddr field is simply used directly as the address of the next microinstruction via transistors 21j; and example in FIG. 8b is the BtoPPL-0 through BtoPP1-3 series. If #JmpCntl(2-0) is nonzero, it indicates which control lines will replace the low order bits of #JmpAddr via logic circuits 21k, and so form the next micro-address on lines 21a. This technique is refered to herein as dispatching, and is readily implemented in MOS technology as seen in the circuit of FIG. 10.

In the example device, a maximum of 256 microinstructions are possible, each consisting of a multi-bit word (outputs 18) in FIG. 6, but a total of only 160 microinstructions are required to implement the Table A instruction set, and so only 160 words of CROM are formed. Each of these is only a 45-bit word, containing a possible forty-five outputs 18 of microinstruction control. Additional microcoded functions for the device (new macroinstructions not in Table A) may be added by implementing a subset of the Table A instruction set, or replacing it entirely. The functions executed may be expanded by using a larger CROM 17, requiring more bits in the address 21a, and for more bits 18 for the output, in other embodiments.

All conditional branching in microcode is accomplished by means of dispatching. A base address is specified in the #JmpAddr(7-0) bits of the microinstruction. The #JmpCntl(2-0) lines indicate which control lines then replace the low order bits of this base address to generate the new microinstruction address on lines 21a of FIG. 10. For example, FIG. 8k depicts dispatching on the IR(3-0) bits, as implemented in the logic circuits 21k of FIG. 10.

The dispatch field bits (like bit-3 to bit-0 in FIG. 8k) actually replace the low order address bits in te #JmpAddr(7-0) field; they are not ORed with them. For example, suppose #JmpAddr was specified to be 00010001, and the #JmpCntl(2-0) lines set to `110`, indicating a dispatch on STC, the status carry bit input to logic circuitry 21m. If STC were `0` the next micro address would be 00010000. The possible dispatch fields implemented in FIG. 10 are summarized in Table E, and each of the dispatch possibilities is further explained below; however, the microinstruction sequences for the illustrative instruction set will be examined.

In FIGS. 8a to 8j, a flow chart of the microinstructions of Tables B and C as executed to implement the macroinstruction set of Table A is illustrated. FIGS. 8a to 8j reference the microinstructions of Table C by name, as well as the CROM addresses of Table C in hex. Table C is only a partial listing of the microinstruction set. Execution of each of the the Table A macroinstructions begins with the instruction acquisition IAQ sequence of FIG. 8a, starting at IAQ-O. Assuming no interupt or reset is asserted, a group disptach is performed on the group field at IAQ-2, selecting one of twenty-four addresses for one of th operand addressing modes or for miscellaneous jumps or traps. These twenty-four alternatives k are shown in FIGS. 8b to 8d. Note that some of the operand fetch microinstructions are shared by several addressing modes, particularly RFtoA-1 (at address 84) which is used by eight different modes or paths, or "immedite-to-A", ItoA-1, at 9F used in five different paths. All four of the B-register-to-peripheral-page BtoPPL microstates are used in the A-register-to-peripheral and immediate-to-peripheral modes. For the general opcodes, after stepping through the operand fetch microstates of FIGS. 8b to 8d for the appropriate addressing mode, a function dispatch is performed, using the low order bits of the instruction word (#JmpCntl=001), to select one of up to sixteen possible functions to execute on the operands which have been fetched; these are shown in FIGS. 8e to 8j and are labelled dual operand function DOPFUN, dual operand function-peripheral DOPFUNP, single operand function normal SOPFNN, single operand function special SOPFUNS, long access function LAFUN, or miscellaneous MISC, all of which end in a return to IAQ-O at CROM address 00. Note that the mneumonic such as ADD, MOV, CMP, etc., is used for the microinstruction for functions in the flow chart of FIG. 8 of FIGS. 8a-8j or Tables B and C as in the microinstruction set of Table A.

Dispatch Modes for CROM Addressing (Refer to TABLE G)

The first type of dispatch is unconditional branching. If no conditional branching of the microcode is desired, #JmpCntl=000. This causes transistors 21j to control for all bits (FIG. 10) and the device branches unconditionally to the microinstruction at the address on the eight #JmpAddr lines 23 after the current microinstruction is executed. The address is formed by the CROM bits in the #JmpAddr (7-0) field of the current microinstruction. This type is used for sequences like BtoPPL-0, BtoPPL-1, BtoPPL-2, etc. of FIG. 8b.

The next type is function dispatch used to select the function at decision points 8n, SOPFUNN, DOPFUN, etc. in FIGS. 8a-8d. Fuction dispatch is defined in Table F. When #JmpCntl=001, the next microinstruction is determined by the low four bits of the IR register. The base address for dispatch is formed in the #JmpAddr(7-0) field of the microinstruction. The next micro address is determined by replacing the bits 3-0 of the base adress with bits 3-0 of the IR register, so the offset can be up to sixteen. To avoid confusion, the base address should be a multiple of sixteen (i.e. the lowest four bits of the base address equal 1 0`). A function dispatch is a dispatch of the "function" field of the instruction word in the register IR. The function field indicates the arithmetic operation to be performed. This is contrasted with the `group` field, bits 7-4, which indicate the addressing mode of the macro instruction (Table A instruction). Even though format "1" instructions have a 3-bit function field (IR bits 2-1-0), the function dispatch still performs a 16-way branch on lower four bits of the IR register. The function dispatch for format "1" opcodes thus depends on the value of the IR(3) bit.

Another type is the test sign bits dispatch. An example is the RJmp-3 microstate of FIG. 8d, decision point 8p. The sign bit which is the contents of bit-7 the T/MAH register, T(7), may be used for dispatch by specifying #JmpCntl=`010`. Two alternative jumps exist here. One is the 8-bit address of the microinstruction to be executed if T(7) is `1`, and the other is the address of the microinstrucion to be executed if T(7) is `0`. The address for T(7)=1 is the address for T(7)=0 plus 1. The address for T(7) =O is loaded into the #JmpAddr field, then 1 is added if the test indicates T(7)=1.

The next type of dispatch is "test if zero". The microcode may test the value on the O bus of the immeidately preceding microinstruction by specifying #JmpCntl=`011`. When this code appears in microinstruction i, it tests the O bus contents of the previously executed microinstruction, i-1. The entry point logic 21 replaces #JmpAddr(O) bit with a bit which is `1` when the O bus is all zeros and `0` otherwise.

Another type of dispatch is "test if interrupt". The microcode tests for a pending interrupt by dispatching on the IACT (Interrupt Active) signal input from the peripheral control circuitry 20. This is accomplished by #JmpCntl=100 in the output 18. This type is used in FIG. 8a at IAQ-1 to branch off to INT-0 if an interrupt is signalled. As with other dispatch instructions, two alternative addresses exist, one (E1) is the microinstruction address of INT-0 to branch to if IACT=`1`, and the other (E0) is the address of IAQ-2 branched to if IACT=`0`; these are adjacent addresses. The IACT line is asserted by the peripheral control circuitry 20 when an interrupt condition is detected. IACT can be asserted only when STINT (Status Interrupt Enable) is `1`. Interrupts may be signalled from the external interrupts -INT1 and -INT3 or the internal timer interrupt, INT2.

Another type of dispatch is "group dispatch". This is done at IAQ2, decision point 8m of FIG. 8a as well as after RFtoA-1 in FIGS. 8b and 8c at decision points 8q. Note that another group dispatch is possible because the opcode is still in IR. Group dispatch is defined in Table E. Dispatching on the group field of the IR register is accomplished by specifying `101` in the #JmpCntl field. The base address field is defined by the #JmpAddr field of the microinstruction. As described above, there are twenty-four groups defined, eight in format 0, IR(7)=0, and sixteen in format 1, IR(7)=`1`. The groups may be numbered as in Table E. The group dispatch performs a 24-way dispatch on the group field by replacing the low order bits of #JmpAddr lines 23 with a function of the group number. The high nibble of the IR register, IR(7-4), is placed in the low nibble of the next address, shifted by one bit. The low order bit of the next address is IR(3) OR NOT IR(7). For format `0` instructions, NOT IR(7)=`1`, and the 0 bit of the next address always `1`. Thus, the machine will jump to a micro address which is the base address plus (group *2) +1 for format `0` group numbers. For format `0` instructions, NOT IR(7)=`0`, and the 0 bit of the next address equals IR(3). Thus, the machine will jump to a micro addresss +IR(3) for format `1` group numbers.

In a group dispatch, the CROM addresses "base address", "base address+2", "base address+4", etc. may be used for other microinstructions; only alternate CROM addresses are used after the 24-way group dispatch. The example microinstruction set of Tables B and C and FIG. 8 uses the group dispatch at IAQ-2 after the instruction is loaded into the IR. Each "group" corresponds to one of the addressing modes, and the microcode executed after the dispatch fetches the appropriate operands for this instruction. A "function" dispatch is then done, and the microcode branches to perform the appropriate ALU operation on the operands. In this manner, the operand fetch microinstructions are shared among the intructions, but each instruction has its own microcode to perform the function of the instruction.

A "test if carry" type of dispatch is also available. The microcode tests the value of the carry bit in status register ST by performing a dispatch on the STC bit. This is indicated by #JmpCntl(2-0)=`110`. The bit tested is the value of the STC or status carry bit after the execution of the immediately preceding microinstruction, i.e. the microinstruction executed prior to the one containing the #JmpCntl(2-0)=110 bits. The STC bit is placed in bit (O) of #JmpAddr, and the result used as the next microinstruction address. If the STC bit is `1`, control transfers to one address, and if STC=`0`, control transfersto the next lower address.

Another available type of dispatch is "test status register" or macro jump. The contents of the status register are tested with this "macro jump" dispatch by specifying #JmpCntl(2-0)=`111`. This dispatch tests eight possible conditions of the status register, indicated by the three bits in IR(2-0). If the condition is true, control transfers to the base address plus 1. If the condition is not true, control transfers to the base address. The conditions tested for macro jump are indicated in Table I. The base address field must be even and is placed into the #JmpAddr field of the microinstruction. The result of the condition test is placed in bit 0 of #JmpAddr to form the new microistruction address. The macro jump dispatch is used in the microcode of Table B and FIG. 8 to implement the conditional branch instruction at RJmp-3, selecting RJmp-4 or -5.

Another type of dispatch is the reset operation, microstate Reset -0 of FIG. 8e. When the RESET pin of chip 10 is asserted (driven high externally), the peripheral control circuitry 20 asserts the RST signal to the CPU. The entry point logic 21 of FIG. 10 immediately forces the next microinstruction address to be hex FF or all ones by transistors 21n, grounding the lines 21a on H1. Unlike the normal interrupt facility, the microcode does not poll the RST line; rather, the microinstruction at CROM address FF is unconditionally forced to be the next microinstruction executed. The sequence of microinstructions RESET-0 to RESET-3 of FIG. 8a executed upon reset results in fetching a subroutine entry point address at address FFFE in memory (in the on-chip ROM 11) and branching to this subroutine.

Addressing Modes For Macroinstructions

The macroinstructions of Table A are shown also in an instruction map of FIG. 9 wherein the most significant half MSH of the instruction is listed across the top and the least significant half LSH is listed down the left side, in binary and hex. Thus, an ADD instruction with an addressing mode of "B, A" has an opcode of 0101000 in binary or 68 in hex; this addressing mode means that the contents of the B register or R1 in RAM 12 is added to the contents of the A register (RO in the RAM) and the sum is written into the A register, so B is the source address and A is the destination address. The B, A addressing mode uses the least possible states in execution, and shares some of these states with several other instructions, such as MOV, AND, OR, XOR, SUB, CMP, etc., all of which have the same MSH opcode of 0110.

The ADD B,A and MOV B,A instructions (and the like) are dual operand instructions using the A and B registers. Also, single operand intructions can use the A or B register; for example the instruction DEC A (opcode=10110010) means decrement the A register, or the instruction CLR B (opcode=11000101) means clear the B register. Instructions in the 1011 column of FIG. 9 operate on the A register, and instructions in the 1100 column operate on the B register (with exceptions as noted), and these are single operand instructions. Generally, the A or B register (or B,A) addressing modes require only five machine states to execute, three of these being instruction acquisition shared by all.

Register file addressing is also available for most instructions; this mode is identified by Rn in FIG. 9, and means that one of the 128 or 256 registers in the registers file RF or RAM 12 is the source or destination address. So, for an instruction "ADD Rn, Rn" the opcode is 00111000 (FIG. 9) followed by two 8-bit addresses of the two registers Rn, Rn used for the source and destination operands; thus three bytes are needed for an ADD Rn, Rn instruction. To execute such an ADD Rn, Rn instruction, ten machine states are used, but the source and destination fetch states are shared with all other similar instructions such as AND, OR, MOV, SUB, CMP, etc., all having a MSH opcode of 0100. Register file addressing with A or B register addressing is used in the MSH columns for 0001 and 0011 opcodes, for all of the common arithmetic and logic instructions. Again, single operand Rn addressing is used for instructions of the Rn or 1101 column of FIG. 9. Thus, "ADD R113,A" means add the contents of A register to the contents of the 113th register in RF or RAM 12 and store the sum in the register R113. "MOV R5, R78" means copy the contents of R5 into R78. "DEC R78" means decrement the contents of R78. Since the A and B registers are in the register file as R0 and R1, these may be used in the Rn, Rn addressing mode.

All of the major instructions can use the immediate addressing mode which is specified by "%n" in FIG. 9, particularly the 0010, 0101, 0111 and 1010 columns for MSH. Immediate addressing uses the contents of a byte following the opcode byte as an operand. Thus, "MOV %98, R123" means replace the contents of register R123 with the hex number 98; this sequence requires three bytes to define, these being "01110010 10011000 01111011" in machine instruction format (object code in binary as actually coded in ROM 11), and the three bytes would be stored in sequential addresses in the ROM 11, accessed in sequence by incrementing the program counter.

Peripheral file addressing specifies one of the PF addresses or registers P0 to P255 (see FIGS. 2 to 2d) as an 8-bit field following the opcode. Thus, the I/O ports A, B, C, D, the timer 26 and the I/O control register 25 may be accessed (depending upon the operating mode), all by the instructions in the three columns 1000, 1001, and 1010 of FIG. 9 containing a Pn notation. For example, the instruction "MOVP A, P2" means copy the contents of A register into the P2 address (timer data).

As seen in FIG. 9, there are five instructions which can use direct memory addressing, these being LDA, STA, BR, CMPA and CALL; in each of these the opcode 10001XXX is followed by two bytes which specify a 16-bit address that contains the operand. Direct memory addressing is specified by an "at" sign @, so "LDA @F47D" means copy the contents of memory location F47D (hex) into register A, or BR @F47D means branch to location F47D.

Another addressing mode is register file indirect; the same five instructions, LDA, STA, BR, CMPA and CALL which can use direct can use register file indirect addressing, and these are in the 1001 column of FIG. 9. This mode is specified by asterisk * followed by the register name. The specified register contains the least significant half of a 16-bit address. The most significant half of the address is contained in the next higher register. Thus, STA *R45 means copy the contents of register A into address hex 43F8 (where R46 contains 43 and R45 contains F8).

These same five instructions LDA, STA, BR, CMPA and CALL can employ an indexed addressing mode in which the address of the operand is the sum of the contents of B register and a 16-bit direct address n. The address n is proceded by @ and following by (B) so STA @ 43F8(B) means copy the contents of the A register into the memory location specified by the contents of B added to the contents of 43F8 (hex). The opcodes for all these instructions start with 1010 as seen in FIG. 9.

The Reverse Accumulator

In a typical microcomputer or microprocessor, the ALU receives source and destination operands at its two inputs, and its output is connected to the location of the destination operand for storing the result. This destination location is, in effect, hardware defined or microcode defined, meaning that it functions as an "accumulator" which is automatically accessed, i.e., it need not be addresed by an address acquired from program memory or the like. This is well suited for general operations; however, for controller functions, where the peripheral file PF of the memory address space of FIG. 2 is often accessed for bit test operation, a "reverse accumulator" is of particular utility. This means that the destination location is defined from a memory address (typically in the program counter) rather than being defined by microcode (such as the A and B registers). The peripheral instructions such as ANDP, ORP, XORP, etc. of the instruction set of Table A and FIG. 9 operate in this reverse accumulator manner. As an example, the ORP A, Pn instruction (opcode 10000100) will be examined in detail. This instruction is two bytes, the first being the opcode and the second being the 8-bit PF displacement or offset defining one of the 256 possible PF registers (the high byte of the PF address is a 00000001 generated by microcode #ONEtAH). The two bytes of the instruction are in sequence in the instruction stream, so they are accessed by PC and PC+1. The ORP A, Pn instruction requires ten states or machine cycles to execute: three for fetch, four for a long read, one to do the OR function, then two for a long write. These ten states are as follows:

    __________________________________________________________________________     Microinstruction Bits                                                                           Operations                                                    __________________________________________________________________________     First Microinstruction (first half of instruction fetch) IAQ-0                 #PCHtAH          PCH Register goes to AH bus                                   #PCLtP, #PAL     PCL Register goes to AL bus via P bus,                                         and to P input to ALU                                         default for N    Zeros to N bus                                                #AluCntl = 0000  Add P to N (zeros), carry in is one, so                       #ShftCntl =      PCL is incremented by one.                                    #ABL                                                                           #OtPCL           The result of the add operation goes                                           back to the PCL register                                      #MCNT            Long Memory Cycle, read (first state)                         #MEMEN                                                                         Second Microinstruction (second half of instruction fetch; interrupts          sampled)                                                                       IAQ-1                                                                          Don't Care       Don't care for AH and AL busses since                         AH, AL           this is second half of long read                              #PCHtP           PCH register goes to P bus for increment                                       of PC high; zero on N bus.                                    default to N     Zeros on N bus                                                #AluCntl = 0000  Add PCH contents on P bus to zero on N                        #ShiftCntl =     bus, carry in is from prior state so                          #ABL             if PCL + 1 generated a carry then PCH                                          is incremented.                                               #OtPCH           Results to PCH                                                #MCNT            Long Memory Cycle, read (second state)                        #MEMEN                                                                         #MDtIR           The instruction coming back on MD bus is                                       loaded into IR                                                #JmpAddr =       Interrupts sampled - if INT then go to                        #JmpCntl =       INT-O                                                         Third Microinstruction (fetch B register - discarded for A Register            instructions) IAQ-2                                                            default AH       Zeros to AH bus for zero page address                         #ONEtAL          00000001 to AL bus for B register                                              address in RF                                                 #ALtP            AL bus to P bus for Pass                                      default N        Zeros to N bus for Pass                                       #ALUCntl =       Pass P bus (AL) using Add                                     #ShiftCntl =                                                                   #ABL                                                                           #OtMAL           Leaves B register address in MAL                                               register                                                      #MEMEN           Short memory cycle, fetch B register                          #MDtT            Store B register contents in T Register                                        from MD bus                                                   #JumpAddress =   Group decision - jump to address defined                      #JumpCntl =      by bits 4-7 of JmpAddr and bits 0-3 of                                         IR.                                                           Fourth Microinstruction (fetch A register, store in T Register) AtoPPL-0       default AH, AL    Produces all zeros on the AH and AL                                           busses for A Register address                                 default P, N, ALU, ShiftCntl                                                                    No ALU operation                                              #MEMEN           Short memory cycle, fetch A Register at                                        00000000                                                      #MDtT            Store A register contents in T register                       #JmpAddr =       Jump to address defined by JumpAddr bits                      #JmpCntl =                                                                     Fifth Microinstruction (first half of fetch of address of destination          operand;                                                                       increment PCL) BtoPPL-0                                                        #PCHtAH          High Address for the next location in                                          memory following the instruction                              #PCLtP, #PtAL    Low Address for next location after                                            instruction, and PCL to P bus for                                              increment                                                     default N        Zeros to N bus                                                #AluCntl = 0000  ALU adds 1 (via carry) to PCL                                 #ShftCntl =                                                                    #ABL =                                                                         #OtPCL           Result goes back to PCL                                       #MEMEN                                                                         #JmpAddress =    Jump to next state                                            #JmpCntl =                                                                     Sixth Microinstruction (second half of fetch of destination operand;           increment                                                                      PCH) BtoPPL-1                                                                  Don't Care, AH, AL                                                                              The address on AL and AH continue from                                         prior state                                                   #PCHtP           Set up PCH for increment                                      default N        Zeros to N bus                                                #AluCntl =       Add 1 to PCH via microcarry from prior                        #ShftCntl =      state if PCL was FF                                           #ABL =                                                                         #JmpAddr =       Jump to next state                                            #JmpCntl =                                                                     Seventh Microinstruction (first half of fetch of destination operand           from                                                                           peripheral page) BtoPPL-2                                                      #ONEtAH          AH address for peripheral page =                                               00000001                                                      #MDtP, #PtAL     AL address for peripheral page comes                                           from prior state (memory fetch of                                              second byte of instruction)                                   default N        Zeros to N bus for pass                                       #AluCntl =       Pass P bus through ALU                                        #ShftCntl =                                                                    #ABL =                                                                         #OtMAL           Result to MAC register so dest address                                         is saved for write                                            #MEMEN           Long memory cycle, first half, to read                                         dest operand                                                  #JmpAddr =       Jump to next state                                            #JmpCntl = 000                                                                 Eighth Microinstruction (second half of fetch of destination operand           from                                                                           peripheral page) BtoPPL-3                                                      Don't Care for AH, AL, P, N,                                                                    The address bus continues from prior                          AluCntl, ShftCntl                                                                               state, and no ALU operation.                                  #MEMEN           Second half of long memory read cycle                         #JmpAddr =       Jump to next state                                            #JmpCntl =                                                                     Ninth Microinstruction (OR function for dual operand, peripheral page)         ORP-0                                                                          #ONEtAH          AH bus has address of 00000001 for                                             peripheral page                                               #MALtAL          Destination operand address goes out                                           from MAL register on AL bus                                   #MDtP            From prior fetch, destination operand                                          comes in to P bus via MD bus                                  #TtN             Source operand goes to N bus from T                                            register                                                      #AluCntl =       ALU performs OR function, carry in = 0                        #ShftCntl =                                                                    #ABL =                                                                         #-LST            Load status as defined for OR                                 #MEMCNT          Begin long memory cycle, write, to store                      #WR              result in destination address                                 #JmpAddr =       Jump to next state                                            #JmpCntl =                                                                     Tenth Microinstruction (second half of long memory write to store              result)                                                                        STAL-2                                                                         Don't Care AH, AL, AluCntl, etc.                                                                The address bus is don't care for the                                          pending long write                                            #MEMEN           Second half of long memory cycle, write                       #MR                                                                            #JmpAddr =       Jump to Inst. Acquisistion IAQ-0                              #JmpCntl = 000                                                                 __________________________________________________________________________

Binary Coded Decimal Operation

The constant register BCD of FIGS. 1 and 7d is not a register at all, but is circuitry to generate a correction constant for binary coded decimal arithmetic operations. The circuit is shown in detail in FIG. 7h. Decimal numbers in this processor are represented with two binary coded decimal digits per byte, with the least significant digit in the least significant nibble, bits 3-0, of a byte. For example, the decimal number 78 would be represented in binary as `01111000`. To perform decimal addition on two BCD bytes X and Y in the ALU 14, the following operations must be performed:

(1) the binary sum of X and Y is computed in ALU 14, with the STC bit carried in on Sp, and the result saved temporarily in RF;

(2) a decimal correction constant is computed by the BCD circuit; and

(3) the correction constant from BCD is added in ALU 14 to the saved result from RF to produce the final BCD sum as an ALU output.

Each of these operations requires a microinstruction cycle.

The STC carry bit is added in order to permit adding multiprecision strings of BCD digits. Decimal subtraction (with borrow) is similar to the above procedure. The binary difference X-Y is first computed, and the correction constant then subtracted from the result.

The proper decimal correction constant and decimal carry out bit is used for decimal addition and substraction. The BCD constant logic of FIG. 7d uses the ALU 8-bit carry Cout on line 14g to produce Ulc, 4-bit half-carry Dout on line 14h, the ALU operation code #AluCntl-3 bit, and the ALU outputs on the 0 bus to derive the correction constant in the logic circuits 15-1 (outputted on bits 1-2-5-6 of N bus by transistors 16m) and decimal carry bit DCout on N5 line 15q. Like the binary arithmetic carry, DCout is `1` if a carry is required after a subtraction. DCout is sent to the status register via line 15q for possible loading into the STC status carry bit.

Three microinstruction cycles are required to perform a decimal arithmetic operation. The timing for this sequence is shown in FIG. 7d'. The first state loads the BCD operands on the P and N busses, and performs the appropriate ALU operations (add or subtract) to produce the binary result. The binary result must be stored in RAM 12 in a temporary register in the register file. The second state reads the saved binary result from the register file and leaves it on the MD bus. This state allows the BCD constant circuit of FIG. 7d to determine the correction constant (and load on N bus) and decimal carry out bit, DCout. The third state loads the binary result on the P bus and the correction constant on the N bus and performs the appropriate ALU operation to produce the correct BCD result. The status register should be loaded by asserting the #-LST bit.

The following microinstructions implement a decimal add with carry. A source operand is added to a destination operand, and the result stored in the destination location (a register in the RAM 12 or RF). It is assumed that initially the T register contains the source operand, the MD bus contains the destination operand, and the MAL register contains the register number of the destination operand.

    ______________________________________                                         Microinstruction Bits                                                                        Operations                                                       ______________________________________                                         FIRST MICROINSTRUCTION (DAC-0)                                                 none (default)                                                                               Place all zeros on AH bus                                        #MALtAL       Place contents of MAL register                                                 (destination address) on AL bus                                  #MDtP         Destination operand from RAM 12 on                                             MD bus goes onto P bus                                           #TtN          Source operand goes onto N bus                                   #AluCntl=0000, #ShftCntl=001                                                                 Add with carry (from prior add)                                  #MEM,#WR      Adder output goes to 0 bus without shift                                       and thus to MD bus, and is stored in                                           destination register whose address is                                          still on AH, AL busses.                                          #JmpAddr XXXXXXX                                                                             Go to CROM address of second micro-                              #JumCntl XXX  instruction                                                      SECOND MICROINSTRUCTION (DAC-1)                                                none (default)                                                                               Zeros on AH bus (always for RAM 12                                             address)                                                         #MALtAL       MAL to AL bus so binary result in                                              destination register is read back                                none (don't care)                                                                            Ignor to P and N busses                                          #AluCntl 0000 Maintain the ALu operation code, but                                           not used                                                         #MEM          Read the binary result at destination                                          address, place on the MD bus                                     #JmpAddr, #JmpCntl                                                                           Go to CROM address of third micro-                                             instruction.                                                     THIRD MICROINSTRUCTION (DAC-2)                                                 none (default)                                                                               Zeros on AH                                                      #MALtAL       Destination address to AL bus                                    #MDtP         Binary result goes onto P bus                                    #BCDtN        Put BCD correction constant on N bus                             #AluCntl 0000 Add with no carry                                                #-LST         Load status register ST with decimal                                           carry                                                            #MEM,#WR      Store BCD result in destination register                         #JmpAddr, etc.                                                                               Go to next microinstruction                                      ______________________________________                                    

For a decimal substract operation, the Add operation in the ALU is replaced with subtract, so the second state subtracts the BCD constant. A carry-in `1` is needed in such case since no borrow is required.

The Self-Refresh Ram

The RAM 12 shown in FIG. 11 consists of 128×8 bits, each bit containing two cells 12c of the one-transistor type as shown in U.S. Pat. No. 4,055,444 made by a single-level-poly N-channel self-aligned process. Each cell 12c has an acess transistor 12d and a storage capacitor 12e. There are thirty-two row lines 12f, and the gates of the transistors 12d for all cells in a row are connected to a row line. The two cells 12c of each bit are connected to opposite bit line halves 12g and 12h, and the folded bit line halves are connected to opposite inputs of one of the thirty-two differential bistable sense amplifiers 12s. The circuit of the sense amplifier includes cross-coupled driver transistors 12i and 12j and two grounding transistors 12m and 12n, generally as illustrated in U.S. Pat. No. 4,198,697 issued to Kuo and Tsaur, assigned to Texas Instruments, except two storage cells 12c are used instead of the traditional storage cells and dummy cells of dynamic RAMs. A sensing operation is initiated by clock H3 turning on high-resistance transistor 12m, then completed by clock H3D turning on longer, low-resistance transistor 12n after a slight delay. FIG. 11a shows the timing of the sense operation. A node 12p is connected to this point for all thirty-two sense amplifiers 12s so there is only one set of grounding transistors 12m, 12n. Depletion-mode coupling transistors 12q connect the bit lines 12g, 12h to the drains of transistors 12i, 12j as in U.S. Pat. No. 4,255,679, issued to Lionel White et al, assigned to Texas Instruments; these serve to isolate the sense modes from the bit lines after initial detection. The bit lines are precharged by transistors 12r, clocked on Q1D of FIG. 11a, and equallized by transistors 12t clocked on Q1D with transistor 12u clocked on boosted Q1D, so the bit lines 12g, 12h will start at very nearly Vcc and well equallized.

The bit lines 12g, 12h are connected through a one-of-4 Y decoder 12y so one pair will be connected to an input/output buffer 12v, in each group. There are eight identical buffers 12v, each having an I/O terminal 12-1 connected to one of the eight bits of the MS bus. For input or write, the bit on MD is applied to the bit lines through a push-pull circuit 12-2 which produces true and complement, clocked on H4 so incoming data is valid during H4 for write, then is gated through transistors 12-3 which have a RAM write control RAMWR from memory control 28 on their gates. For RAM read operations, the I/O buffer 12-3 includes a bistable intermediate output buffer comprising driver transistors 12-4 shorted to ground on H2 by parallel transistors. The bit lines 12h, 12g, gated through select transistors 12z in the Y decoder 12y, are connected to input transistors 12-5 for the I/O buffer. The output is taken at the drain of one transistor 12-4 and gated through a transistor 12-6 on the RAM read signal RAMRD from memory control 28; output mode 12-7 is precharged to Vcc on H2 and conditionally discharged by the transistor 12-4 when 12-6 turns on by RAMRD. A transistor 12-8 then conditionally discharges this bit of the MD bus, starting at H4 when the drains of transistors 12-5 go to Vcc.

The use of the two cells per bit RAM configuration instead of dummy cells is especially important in a microcomputer, as distinguished from a stand-alone dynamic RAM, because of the large number of other high level signals existing on the chip, creating a high noise level. The noise margin is enhanced by the two-cell balanced layout. Otherwise, using a conventional DRAM one-T cell with dummy cells, the noise margin would not be acceptable; for this reason, static cells have been traditionally used in microcomputers.

The X or row address supplied to the X decoder 12X comes from one of two sources; the AL' bus for normal read or write access, or the refresh counter 31 for refresh. The refresh counter is shown in detail in FIG. 12 with the multiplex circuit 32. The 5-bit RAM X address on lines 32a comes directly from the AL' lines through multiplexer 32 if a refresh signal -REF from memory control 28 is inactive (high). If -REF is active (low), the five-bit output 31a of the refresh counter is used. The refresh counter 31 contains five shift register stages 31b, each with two inverters 31c, gated on H2 by transistors 31c. Interstage coupling by transistors 31d occurs if a refresh-shift signal occurs on line 31e. Recirculate occurs if transistors 31f are gated on by a refresh-shift bar signal on line 31g. In every machine cycle, one of these must occur during H4 as established by logic circuit 31h which generate the refresh-shift from the -REF signal. Thus, if -REF is present the counter 31 advances after the current address goes via lines 31i to the multiplexer 32. If -REF is inactive, the count holds as recirculate transistors 31f turn on. The feedback bit for the counter is generated by a logic circuit 31j as is conventional pseudorandom shift counters.

The Operating Modes

With reference to FIG. 2a, the primary operating mode of the microcomputer 10 of FIG. 1 is the microcomputer mode in which all of the memory is contained within the ROM 11 and RAM 12. The device is initiallized by RST or reset to be in the microcomputer mode; that is, zeros are placed in the bit-7 and bit-6 of the I/O control register 25. In this mode, only nine bytes of the peripheral file PF are used, the remaining 247 have no function. The peripheral register numbers P0, P2, etc., and hex addresses of the peripheral file registers for the microcomputer mode are shown in FIG. 2a. Port A is used only for input and port B is only an output, while ports C and D are either output or input; thus, registers P9 and P11 define the direction of data in the ports C and D, but no such control registers are needed for ports A and B as they are unconditionally input or output. The port A, B, C, D data registers are contained within the buffers 30 and are accessed by the MD bus, using addresses 04, 06, 08 and 0A (in hex) on the AL bus and page-one or 00000001 on the AH bus. Similarly, AL addresses 09 and 0B access the control registers contained in buffers 30 for ports C and D. A "0" in the control register bit sets the port for input and a "1" sets it for output. An address applied to AL and AH in the unused areas will produce no meaningful result, so the ROM 11 program is of course written to avoid these addresses.

In FIG. 13a a system containing an eight digit diaplay 13-1 and a keyboard matrix 31-2 is shown which uses the device of FIG. 1 in its microcomputer mode. The C port outputs are used for the segments of the display and the B port outputs drive the digits of the display 13-1 and columns of the keyboard matrix 13-2 as illustrated in U.S. Pat. Nos. 3,988,604, 3,921,142 or 4,158,431 for example. The rows of the keyboard matrix 13-2 are applied to the A port inputs. A 8×8=64 key matrix is possible, but ususally less are needed. Other activators and sensors such as in the microwave oven controller of the Van Bavel U.S. Pat. No. 4,158,431, assigned to Texas Instruments, may be connected to the D port as inputs or outputs. An example of a program for display scan in the system of FIG. 13a is is seen in Table J.

In the peripheral expansion mode of the memory map of FIG. 2b, the peripheral page 0100 to 01FF, 256 bytes, is utilized for off-chip accesses. The C port is used as a multiplexed 8-bit address/data bus, and four bits of the B bus are dedicated as control lines ALATCH, R/W,-ENABLE and Clock Out as illustrated in the system of FIG. 13b. This system employs the microcomputer 10 of FIG. 1 as the main processor in a system which uses two other attached processors. One is a video display processor 13f as described in U.S. Pat. No. 4,243,984 issued to Guttag et al, assigned to Texas Instruments. The other is a general purpose interface bus adapter chip 13g which allows the chip 10 to inteface with a standard IEEE 488 bus 13h. The chip 10 produces an 8-bit address on the C port which is latched into an 8-bit latch 13i by the address latch signal ALATCH on port B4, then the address is available on an address bus 13j for the chips 13f and 13g when the enable signal on port B6 goes active. The chips 13f and 13g are synchronized with chip 10 by the clock output on port B7. The C port is then used for data from or to the chip 10 and chips 13f and 13g, depending upon the read/write control R/W on port B5. The chips 13f and 13g are thus configured to respond to addresses 0108, 0109 and 010A to 01FF on busses AL and AH. The AH bus of FIG. 1 will always contain 01 in this mode for off chip accesses, of course. The A port functions as an input and the D port as input or output in this peripheral expansion mode, so other functions are executed aside from accessing the chips 13f and 13g; for example, actuators and sensors, or a keyboard matrix as in FIG. 13a may be used here also.

The full expansion mode of FIG. 2c and FIG. 13c provides the 8-bit address output on C port as in FIG. 13b plus another address byte on D port which may address a memory chip 13k, for example. The full expansion mode allows a full 64K (two bytes - C port and D port) of off chip address range; addresses 0108 to EFFF are available for off chip access. As above, port B at address 0106 provides the memory control and clocking on bits B4, B5, B6, B7. The memory chip 13k may be a 32K device, for example, and the lower byte address from C port is latched at 13i while the high byte goes directly to the chip 13k on lines 13m. The data bus 13n going to the C port is shared by the chips 13f, 13g and 13k. The system of FIG. 13c thus has much greater program capability, compared to that of FIG. 13b, but the D port is not available for other I/O. A keyboard matrix 13-2 could be connected to the remaining four bits of the B port (address 0106, bits 0-3) and the A port as shown, however.

The microprocessor mode of FIG. 2d allows the chip 10 of FIG. 1 to ooperate as an 8-bit microprocessor; all of the addresses in the range 0108 to FFFF are available for off chip accesses. This mode functions the same as the full expansion mode of FIGS. 2c and 13c except there is no on-chip ROM for program memory; actually the chip contains a ROM 11 but it is not used, so if the ROM code built into the device is not correct then the chip can still be used as a microprocessor in this mode instead of a microcomputer, in which cases addresses FOOO to FFFF are treated as external memory locations. The system of FIG. 13c may use the chip 10 in the microprocessor mode, in which case the memory chip 13k could be 64K instead of 32K bytes.

The system emulator mode of FIG. 2e facilitates the development of new ROM 11 programs. All on-chip ROM and peripheral file PF is disabled so all addresses 0100 to FFFF access off-chip locations. This mode permits inexpensive development of new systems by allowing the developer to emulate the desired on-chip ROM 11 code, I/O and interrupt structure with temporary external memory chips 13q and logic 13r of FIG. 13d. The system emulator mode is enabled when the MC pin is tied to a high voltage source (+12v). The memory inteface operates just like the microprocessor mode of FIGS. 2d and 13c except for the peripheral file PF and pin out. The C and D ports are for addresses and data as in FIG. 13c, but the A port is not used (it is emulated off-chip, so the keyboard of FIG. 13c, for example, would be connected to the logic 13r). Pin B3 is an interrupt acknowledge line, pins B4 to B7 are used as before, and pins B0 to B2 are not used (emulated off-chip). The CPU 13 in a chip in the emulator mode functions just as if the on-chip ROM and PF is being used, but addresses asserted on the busses AH', AL' result in off-chip access.

Memory Control

The function of the memory control logic is to control the addressing and timing of all peripherals and all memory expansion modes. The memory control circuitry consists of the circuitry contained in the memory control block 28 in FIG. 14 and the group decode 27 block in FIG. 14. The group decode circuitry 27 handles all the addressing by: (1) decoding the address lines AH' and AL' to determine which internal peripheral, if any, is being addressed (i.e., the RAM 12, ROM 11, INTERRUPT, TIMER, PORTS A, B, C or D) and (2) determine based on which expansion mode that the processor is currently in, if that peripheral exists internally. The group decode 27 outputs of this circuitry are active low and identify which peripheral is being addressed. FIG. 16a illustrates the decoding of the address AH' and AL' and other inputs to group decode 27 as a to specify an internal peripheral. FIG 16b illustrates the group decoder 27 as a circuit implementation of FIG. 16a. The group decode circuitry includes a programmable logic array 802 that interfaces to the address bus AH' and AL' and external signals MMDO, MMD1, EM and MP from the interrupt logic circuitry 29 and #MEM from the CPU 13. The address low bus AL gated through the address buffer 19 to AL'; forms BADD (0-7), and these bits are inputs to the PLA 803. The output of the group decode circuit 27 of FIG. 16b is the GRAM, GROM, etc., signals which cause the selected one of the internal peripherals to be accessed during a machine state. The is a microinstruction control bit obtained from the microinstruction word and it signifies a memory operation. Note that in FIG. 16a MEM must be low or active for any of the internal peripherals to be accessed. EM and MP are derived from the interrupt logic circuitry to be discussed. EM specifies an emulator mode and MP specifies the microprocessor mode. MMDO and MMD1 are memory mode bits (bits 6,7 of the register 25) which are internally programmable and determined the current memory expansion mode. FIG. 16c illustrates the five memory expansion modes determined by the external memory configuration pin MC and the two internally programmable memory mode bits MMD 1 and MMDO in the control register 25. Referring back to FIG. 16b, it should also be noted that the circuitry coupled to line marked PG1 and Z7T4 are implemented for logic reduction purposes. In other words, PG1 is a reduction of an address (F, E, D, E, B, A, 9 and 8) gated into the address for Z7T4 and PGI. Z7T4 is a logic reduction of 7, 6, 5, 4 and signals EM and MEMP where MEMP is the signal MEM inverted and clocked by phase H1. The group decode PLA 802 outputs into a set of devices 800. These are devices that will raise the EXT line when either the RAM, ROM, interrupt circuitry, timer circuitry, or A or D ports are accessed, or during the peripheral expansion mode when an external peripheral is being addressed on the peripheral page PF. The group decode PLA 802 further terminates into a set of gates 801. These are NAND gates that NAND the respective enabling signal from the PLA 802 with a signal MEMH1CNT which is the memory control signal from the microinstruction clocked by H1 and inverted. This signal is produced by the memory control circuitry 28 illustrated in FIG. 16c. The circuitry 803 in FIG. 16b also includes an input signal labeled WRP. This signal originates from the memory control circuitry 28 illustrated in FIG. 16c and is simply the inverted microinstruction bit #WR clocked by H1 (signifying a read or write). In addition to producing the EXT signal as previously discussed, this circuitry also produces the SC signal which signifies a single chip mode of FIGS. 2a or 13a and is used in the memory control circuitry illustrated in FIG. 16c. DADDOUT, produced by gates 804 which NOR the signals MP and MMD1, is a signal that is used in D port to signify the peripheral expansion mode or the single chip mode, thus allowing data to be output on the D port. EXT is functionally

    EXT=GRAM+GROM+GI+GT+GA+GB+GC+GD+INT+EXTT-

where

    INT=(MMD0×PG1)+MP+MMD1 and

    EXTT=MEM+(EM×WR)=EM×MEM×WR+MEM×WR

where PG1 - not page 1 (AH:AL≠01XX)

MMD1--active in full expansion mode, MP=EM=MMD0=0

MMD0 - active in peripheral expansion mode, MP=EM=MMD1=0

EM - active in emulator mode, MC pad=high voltage, MMD1, MMD0=don't care

MP - microprocessor mode, MC pad=1 and MMD1, MMD0=don't care

EXT has two functions: one is to allow ENABLE, which is one of the external memory controls (output from port B6). The second function is to allow port C to read the external peripheral onto the MD bus via EXTRDH4.

FIG. 16c illustrates the remaining memory control logic circuitry 28. Referring not to top of FIG. 16c, the EXT signal inputs to this logic circuit from the group decode circuitry 27 previously discussed in FIG. 16b. EXT is used to produce EXTC, clocked in by H2, which is used in port C circuitry and ENABLE, by both H3 and H1, which is used in the port B logic circuitry. EXTC is used by the port C logic to enable the port to perform an external read during the time phase H4. ENABLE is used by Port B as an external memory control during all modes except the single chip mode. The remaining memory control logic circuitry receives three microinstruction bits 18 which are #MMCNT, #WR and #MEM, illustrated in the timing diagrams in FIG. 4. #MEMCNT is used to produce LDADDR which is the load address signal for the address buffers 19 in FIGS. 1 and 7a. #MEMCNT (memory continue) is also used to produce the MEMH1CNT signal used in the group decode logic, FIG. 16b. This memory continue signal is also used to produce ALATCH with phase H4. ALATCH is used by the Port B logic as an address latch signal in the peripheral expansion, full expansion microprocessor and emulator modes. The #WR microinstruction control signal which is high for memory regards and low for memory writes is used in producing the OtM signal sent to the CPU 13. The OtM is a signal that goes to the CPU and connects the O bus to the MD bus allowing the ALU to write onto the MD bus. This connection is made: (1) during the first state of a long memory cycle or (2) during a writing mode. The OtM signal is an OR of the memory continue line #MEMCNT and read/write line #WR. The read/write microcontrol signal #WR is also used to produce WRRAM and WRRAM which is used by the RAM logic of FIG. 11 for read/write operations. LNGWR is produced by the memory control and read/write microinstruction lines and is routed to ports B, C, D, the interrupt logic and the timing logic. This signal is used to designate long read or write cycles.

CDATAOUT is produced in the circuit 28 of FIG. 16c by the single chip mode signal SC produced by the group decode logic 28 as mentioned previously and the memory continue line clocked by H1. CDATAOUT allows port C to output the contents of the C data latch in the single chip mode and output an address in the first state of a long read or write cycle. PTCOUT places port C into an input mode for the second state of all long read cycles or in other words, port C is placed into the output mode in both states of a long write cycle. When in the single chip mode, PTCOUT is disabled and the contents of the port direction latch determines the port direction.

    PTCOUT=SC+(WR-x MEMCNTd)

where MEMCNTd is delayed nd stretched form of #MEMCNT (memory continue from microinstruction) that goes high in H1 of the second state of long memory cycles and lasts until H2 of the state following the long cycle.

The next signal produced by the memory control logic circuitry of FIG. 16c is REF which is transmitted to the RAM multiplex 32 and notifies the RAM refresh multiplex 32 and coounter 31 that it may execute a refresh cycle using the address in the 5-bit row refresh counter 31. This signal causes the RAM address multiplex 32 to pass the refresh counter 31 contents rather than the bus address AL' to the RAM 12. It also increments the refresh counter 31 by one state. REF will occur (1) during any non-memory cycle, and (2) during the first state of any long memory cycle.

    REF=#MEM+#MEMCNT

INTACK is produced by the memory control circuitry and is sent to the interrupt logic. INTACK (interrupt acknowledge) is produced by the microcode during the interrpt microroutine and tells the interrupt logic to place a vector on the memory data bus MD, identifying the highest priority interrupt active, i,e., flag set. (INTACT=#MEM×#WR.)

INTAX is a signal that is logically equivalent to INTACK but is output from port B in the emulator mode and is further clocked by H2.

BAO produced by the memory control circuitry 28 is transmitted to the I/O ports and the timer and is simply a buffered contents of the 0-bit of address bus AL'.

The last signal produced by the memory control circuitry of FIG. 16c is CNTLH1 which is the H1 phase with #MEMCNT from the microinstruction.

Interrupt Logic Circuitry

The microprocessor system has the capability to receive two external interrupts INT-1 and INT-3, one internal timer interrupt INT-2 and a reset signal RST. When an interrupt is received by the interrupt logic 29, the peripheral hardware 20 asserts the IACT signal on a control line 29a (FIG. 17a) to the CPU 13. The CPU 13 may then read an interrupt vector supplied by the peripheral control hardware 20 on to the memory data bus MD, indicating which interrupt has occurred. The interrupt vector read requires two cycles, as shown in the timing diagram in FIG. 4. It should be noted in FIG. 4 that both #MEM and #WR must be low during both cycles of the interrupt vector read. Like a long memory read, the vector is not available until the end of the second microinstruction cycle as seen in FIG. 4. The value of the vector supplied by the peripheral circuitry 20 for each interrupt is shown in FIG. 17d. There is a difference between the trap vector supplied by the peripheral control circuitry 20 and the trap vector address at which the interrupt subroutine entry point address is stored. The trap vector supplied by the peripheral circuitry 20 is the same as the "TRAPn" opcode for the processor's Table A instruction set. In order to call the interrupt handler, service routine the microcode must generate the trap vector address from the vector (FIG. 17d) supplied and read memory 11 at that location to get the address of the interrupt handler subroutine.

Interrupts can be recognized only if the interrupt enable flag STINT in the status register ST of FIG. 7e is set. If the flag is cleared, no interrupts will be recognized. Each interrupt can also be individually enabled and disabled in the I/O control register 25 of FIG. 17b, the contents of register 25 being seen in FIG. 17c. The I/O control register 25 is mapped into location PO of the peripheral file PF, FIG. 2. The memory expansion mode, individual interrupt masks, and individual interrupt sets are controlled through this register 25, FIG. 17b, by writing the appropriate bits via MD at location P1, activating transistors 25a. The interrupt sources may also be individually tested by reading the interrupt flags via MP at address P1, activing transistors 25b. The interrupt flag values are individually tested by reading the interrupt flags. Interrupt flag values are independent of the interrupt enable values as shown in the interrupt logic circuitry of FIG. 17a and 17b. FIG. 17c illustrates the contents of the I/O control register 25 for a read operation or for a write operation. Writing a "1" to an interrupt clear bit location in the I/O control register will clear the corresponding interrupt flag. The interrupt flag is unaffected if a "0" is written to the interrupt clear bit. Once the interrupt is recognized, the status register ST and program counter PCL, PCH contents are pushed on the data stack; the starting address of the interrupt routine is then fetched from the memory location as shown in FIG. 17d. The interrupt enable status bit STINT is automatically reset after the interrupt is recognized. It is automatically restored by the interrupt return instruction; it can also be set or reset by program control. The interrupt source can be determined by testing the I/O control register 25 illustrated in FIG. 17c. Interrupts 1 and 3 are externally generated as previously discussed. The timer interrupt, interrupt 2, is generated internally and can be reset in the I/O control resister 25.

The external interrupt, interrupt 1 and interrupt 3, can be configured to be either level or edge triggered. At the falling edge of interrupt 1 or interrupt 3, the corresponding flag bit in the I/O control register 25 is set independently of the state of the interrupt enable bit. The interrupt then remains pending until the interrupt input returns high, and the interrupt flag bit is cleared. Referring to FIG. 17a, interrupt 1 is input on the interrupt 1 pad 29b through a Schmitt trigger for squaring the waveform, then is clocked by H3 and H2 into a network of invertors and devices clocked by H1 and H4 in order to latch the input into a series of NOR gates 810 which produce the interrupt flag signal on line 29c. Therefore, a single low pulse on the interrupt pad is sufficient to set the interrupt pending flag 29c and whenever this interrupt is acknowledged, the flag will be cleared by the INT1VCL signal input 29d into the NOR gate circuitry. If on the other hand, a level "low" is applied to the pad, the flag is set, and will remain set (even if acknowledged) until the level is removed. If the interrupt is acknowledged while the level is still present, the level edge detect latch 810 is cleared even though the level is still present and if the level is removed then no interrupt will be pending. INT1VCL is produced by either an interrupt acknowledge or by writing a "1" to the interrupt clear bit in the I/O control register 25. INT1VCL clears only the leading edge detect circuitry and will not clear a pending interrupt if the level is produced. Therefore, if the leading edge latch is cleared and the level is present, the interrupt flag will be set. However, if the leading edge latch is cleared and the level is removed, the interrupt will no longer be pending. Since the interrupt is pending if the flag bit is set, a pulsed interrupt can be easily detected and serviced. The interrupt is reset as soon as the interrupt flag bit is cleared since the interrupt is pulsed and automatically returns to the high or inactive state. The interrupt/enable must not be reenabled sooner than the maximum pulse length of the interrupt. Multiple level sensitive interrupts may be wire ORed on an interrupt input since the interrupt input will remain pending until all interrupt sources are reset, thus allowing the input to return to the inactive state. If multiple interrupt requests are enabled and pending, then the interrupts will be serviced in the order shown in FIG. 17d.

Referring back to FIG. 17a, the interrupt 1 flag INT1FLG signal on line 29c is produced by the inverter 811 and transmitted through a network of devices 812. This network of devices compares the inputs of the interrupt flags with the interrupt enable signals, the set interrupt signal together and the emulator mode signal. If the interrupts have been enabled, i.e., STINT inactive, and a particular interrupt flag signal is active together with this enable signal, the signal IACT (interrupt active) becomes valid on line 29a. This signal goes to entry point circuit 21, but a microjump on this signal is not performed until after the second state of the instruction acquisition IAQ1, FIG. 8. Since this jump is performed into an active interrupt flag, the control ROM 17 will later cause an interrupt acknowledge signal INTAC to be produced in the memory control logic of FIG. 16c. This signal causes the interrupt logic to place a vector on the memory data bus MD corresponding to the highest priority interrupt present. At the same time, the edge protecting latch corresponding to the accepted interrupt is cleared. If more than one interrupt request is made, the highest priority interrupt is accepted and then cleared, but the unaccepted interrupts are not cleared.

Referring to FIG. 17a, the interrupt 1 flag on line 29c is also transmitted through the devices 812 into a NAND gate in logic 814 where it is combined with the interrupt "1" (INT1EN) in gate circuitry for prioritization where interrupt 1 has the highest priority. These signals are then combined with a NAND gate to produce INT1VCT on line 29e and INT1VCT (interrupt 1 vector clear) and the vector address for the interrupt service routine which is placed on the MD bus by transistor 29f, this adders being 11111101 or FD.

The second interrupt is obtained from the timer and input into the interrupt logic circuitry device network 812 at line 29g as shown in FIG. 17a. The remaining processing of this interrupt flag is similar to the interrupt "1" flag processing in that it is input into the interrupt 2 prioritization circuitry 815 and when enabled loads the vector address (11111110) for the interrupt service routine on the MD bus by transistor 29h and activates IN2VCT (interrupt 2 vector clear) on line 29i.

Interrupt 3 is input on the interrupt 3 pad as shown through Schmitt trigger circuitry similar to that for interrupt "1". However, interrupt 3 has a dual purpose. In the nonemulator mode, interrupt 3 is a maskable low priority interrupt that can either be edge or level triggered. This is accomplished in a manner similar to that for interrupt "1" in that the NOR gate network 813 is similar to the operation of the NOR gate network 810. The additional circuitry for interrupt 3 produces the signal TDTCH2 at line 29j which is input to the timer circuitry to be discussed. The interrupt 3 flag on line 29k is input into prioritization circuitry 816 to produce INT3VCT on line 29m (interrupt 3 vector clear) and the appropriate vector address.

It should be noted that circuit 817 is used to load bits 2 through 7 on the MD bus via transistor 29n when an interrupt vector address is loaded. Three bits are also loaded in the system emulation mode when an external interrupt is received.

The reset pad of FIG. 17a is the input for the reset signal. When the reset pin is asserted externally, the peripheral control circuit 20 asserts the reset signal to the CPU. The entry point logic 21 immediately forces the next microinstruction to the hex FF address via transistor 21n of FIG. 10. Unlike a normal interrupt facility, the microcode does not pole the RST line; rather, the microinstruction at the control ROM 17 address, hex FF, is unconditionally forced to be the next microinstruction executed. In other words, this address is jam set. The insertion of Reset causes the following actions: By hardware the I/O control register 25 bits 6-7, the two most significant bits (memory mode control), are reset to "0"; the port data direction registers for the ports are loaded with all "1's" thus forcing bidirectional I/O ports to the input mode; All status register ST bits are cleared, and the stack pointer SP is initialized to a value of "1"; This is done by the microinstructions RST-0 to RST-3 of Table B and FIG. 8, and circuitry as indicated. The remaining registers in the I/O function must be initialized by the reset service routine as required. Reset must be held active on the reset pin for a minimum of 5 clock cycles to guarantee recognition. When it is removed, the reset function is initialized. Thus, the reset input requires no external synchronization. Referring to FIG. 17a, the reset signal is transmitted through a Schmitt trigger as before to a network which produces the RESET signal on line 29r used in circuitry shown in FIG. 17b, RESET, on line 29s which is set to the I/O ports and RST on line 29t which is sent to the entry point logic 21. In addition, when the MC pad is set to 12 volts, reset is transmitted to the internal clock 33 so it synchronized via the "CLKSYN" line 29u.

The mode control MC voltage is also input into the interrupt logic circuitry of FIG. 17a as shown via the MC pad. This voltage goes into a circuit 29v to detect high voltage input (i.e., 12 volts) to produce the EM signal on line 29w which indicates the emulator mode. A normal "1" or Vcc=5 v on the MC pad will produce the MP signal or microprocessor mode signal on line 29x. Both the EM and MP signals are transmitted to the memory control circuitry 28. The EM signal in addition is transmitted to the port B logic into the circuitry shown in FIG. 19b. In addition, the emulator mode signal is used in the device network 812, together with the interrupt 1 and 3 flag as previously discussed.

Referring to FIG. 17b, the I/O control register 25 is illustrated interfacing to the MD bus. It should be noted that there are two inputs from the memory control logic, GI and LNGWR. These two inputs are used to designate access to the I/O control register 25 via MD bus and a read or write operation in conjunction therewith. The line INTWRH4 going to gates of transistors 25a is produced by the NOR of LNGWR and GIP from the memory control circuitry. This signal is clocked through a device when a write operation is performed. In a similar manner, the signal INTRDH4 going to gates of transistors 25b is produced from the NOR of GIP and RWRI which is a derivative of LNGWR signal from the memory control circuitry 28. This signal (likewise clocked by H4) signifies a read of the I/O control register 25. The contents of the I/O control register is illustrated in FIG. 17c. The circuitry 820 of FIG. 17b serves as a inverter storage latch for the interrupt "1" enable signal. This strorage cell can be written into when INTWRH4 is active and the "0" bit of the MD bus is active. Likewise this signal can be read when the INTRDH4 line is active. This signal is then read by examining the "0" bit on the MD bus. The MD bus bit position "1" on a read cycle is devoted to the interrupt "1" flag. The interrupt "1" flag signal is derived from the circuitry in FIG. 17a as previously discussed. When the interrupt "1" flag is to be read, the INTRDH4 line should be active, thus allowing the contents of the INT1FLG line to be input on the bit 1 of the MD bus. In the write mode, a bit written at this position will be interpreted as a clear of interrupt "1". Therefore, in the write mode the circuitry 821 will serve to produce the INTVCL signal which serves as a clear signal for interrupt 1 flag 29c. Specifically the circuit receives the signal INTWRH4 to signify a write operation along with the bit "1" position of the MD bus, but "1" is input into a NAND gate with INT1VCT and transmitted through a device and clocked by H4 into a NOR gate with an input from the emulator signal to produce the interrupt/clear signal, INT1VCL. As previously discussed, the interrupt/clear signal will provide a clear to the edge latch detecting circuitry. However, if the interrupt is a level interrupt, and the level is still active (i.e., low) the signal will not clear the interrupt. Therefore, the flag will still be set. The circuitry associated with MD bus bit position 2 is similar to that for the MD bus bit position "0" (i.e., circuitry 820) and will not be discussed. Likewise the circuitry for bit position 3 is similar to the circuitry for position "1" with the exception of the fact that there is no NOR gate to receive the clear bit transferred through device clocked by H4; instead there is an inverter. However, the interrupt flag circuitry is the same. The circuitry associated with bit position 5 and bit position 4 for the MD bus is similar to the circuitry for bit position 1 and bit position 0, respectively, and will not be discussed. The register 25 of FIG. 17b is part of the strip and is in a regular pattern with inventers 15i and feedback transistors 15j just like the registers 15 of FIG. 7b; the MD bus is a continuation of the eight metal lines of FIG. 3, and the control lines to gates of 25a, 25b are polysilicon.

Bit position 7 and bit position 6 of register 25 are dedicated to storage of the MMD1 and MMD0 bits. The MMD1 bit is stored in the circuitry of 823 and outputted via circuit 824. Note that the combination of these two circuitries is effectively a master slave latch as in 820 with the exception of a NAND gate 25g which allows this circuitry to be reset when the reset condition is present. This reset condition is obtained via line 29r from the circuitry in FIG. 17a. It should also be noted that read or write operations can be performed on MMD1 or MMD0.

In emulator mode interrupt 3 becomes a non maskable interrupt (no enable required) and interrupt 1 is a maskable interrupt enabled only by STIT.

Programmable Timer/Event Counter

The programmable timer/event counter will be described with reference to FIGS. 18a-18e; this device is an 8 bit binary counter with a programmable prescaled clock source as shown generally in FIG. 18d. The basic elements comprising the programmable timer/event counter are: (1) a fixed divide-by-8 pseudorandom shift-counter 26 for which the output .0./8 is an internal input 26i divided by 8; (2) a 5-bit prescaler 26a (binary decrementor) which resides in the memory map of FIG. 2a as part of the timer control register at P3, represented by latch 26a' of FIG. 18d (these 5 bits of 26a' are write only); (3) A 5 bit control latch (write only) 26a-1; (4) 8 bit time value register (timer decremeter) 26; (5) 8 bit timer latch 26b; and (6) an 8 bit capture latch 26c.

The two accessible locations P2 and P3 (FIG. 2) for the timer function differently at read vs. write, as seen in FIGS. 18e. The location P2, "timer data" contains an 8 bit, write-only latch register 26b-1 and an 8-bit read-only register 26b-2. Note during a read operation, the location P2 will contain the instantaneous count-down value. FIG. 18e shows the control register at location P3; here, for write, bit position 7 is the "counter start" command position. A "1" written in bit position 7 will immediately start the timer. Bit position 6 of FIG. 18e designates the timer source. A "1" in bit position 6 selects the internally generated PHI/8 (internal clock frequency divided by 8) clock; a "0" selects the external clock source obtained from bit position 7 in the A port. Bit positions 4-0 of the control register 26b, location P3, contain the prescaler 26a latch value for a write operation. For a read operation, all 8 bits of the timer control register of FIG. 18e contain the capture latch value. FIG. 18e illustrates the contents of the timer data register P2. Note that in the read mode, the current timer value will be read. However, in the write mode the data written will determine the current latch value. Any number from 0 255 can be written into the timer latch. Likewise, the prescale latch can be loaded with any number from 0-31. Thus, the device can count any number up to 256×32=8192. The timer source bit position 6 and a start/stop bit position 7 are also reloaded when loading the prescaler 26a. As long as the start/stop bit is equal to "0", neither the prescaler nor the timer can be decremented, thus stopping the timer. Whenever a "1" is written into the start/stop bit position (regardless of whether it was previously a "0" or "1") the following happens: (1) the 5 bit prescaler latch register 26a-1 (that was loaded together with the start/stop bit position) is transferred into the prescaler value register 25a. The value register 26 a for both the prescaler and the value register 26 for the timer are registers that do the actual decrementing. The latch, or capture registers 26a-1 and 26b, do not decrement. The timer latch register 26b is also loaded into the timer value register 26 upon start. The divide by 8 logic (.0./8) value is reset to its initial state. The decrement clock inputs to both the prescaler 26a and the timer value register 26 which are then enabled. The timer, whether in internal or external mode, is prescaled by the 5 bit binary counter 26a. The prescaling value is determined by the least significant 5 bits of the timer control register P3, FIG. 18e. The actual prescale value is equal to the timer control register prescale latch value 26a-1 plus 1. Thus a value of hex 88 in the timer controller register (i.e. start=1, source=0, prescale=8) would result in a PHI/72 clock output from the prescaler 26a. The prescaler clock is then used at input 26i to decrement the counter 26. The interrupt 2 flag in the I/O control register 25 is set each time the counter value 26 decrements past the 0 value. The prescaler 26a will count down past 0000 at which time the timer value register 26 is decremented 1 count via 26i and the prescaler value register 26a is reloaded with the contents of the prescaler latch register 26a-1. The timer 26 continues to be decremented in this fashion until it counts past hex 00 at which time the timer/interrupt flag (interrupt 2 flag) is set to "1" in the I/O control register 25 and the timer value register 26 is reloaded from the timer latch register 26b starting the full time period over again. If at any time during the countdown period, the timer control register bit position 7 change from "1" to a "0", the timer stops, ceases decrementing. Upon timer start (a "1" in bit position 87 of the timer control register P3) both the prescaler and timer value register 26a, 26 are reloaded with the full latch contents 26a-1, 26b and the system begins to count normally again. Note that there is no way to stop the timer in progress and resume time from where it stopped.

When the timer is in the event counter mode (timer control register bit position 6=1), the counter functions as above except bit position 7 of I/O port A is the decrementing clock source. A positive edge transition on port A bit 7 decrements the count chain. Note that port A bit 7 can function as a positive edge triggered interrupt by loading a start value of "0" into both the prescaler 26a-1 and the timer latch 26b. This timer mode can also be used as an externally clocked, real time clock if the external clock is input to port A pin 7. The maximum pulse frequency should on port A, bit 7, in the event counter mode must not be greater than PHI/8.

Another feature that exists in this timer is the capture latch 26c. This register 26c is loaded from the timer value register 26 whenever the interrupt is active. At the falling edge of interrupt 3, the timer value is loaded into the capture latch. When read, the timer control register P3 contains the capture latch 26c value. This capture latch feature provides the capability to determine when an external event occurred relative to the internal timer and is ideally suited for pulse width measurement. Note that if an interrupt is not desired, interrupts should be totally disabled by the interrupt enable bit or the individual enable bit for interrupt 3 should be disabled.

Since the interrupt 2 flag is raised only after the timer has decremented passed "0" for a given count of N (or division by N), a value of N -1 must be loaded into the latch registers (prescaler 26a-1 or timer 26b).

The actual circuitry for the programmable timer/counter is illustrated in FIGS. 18a, 18b and 18c. Referring now to FIG. 18a, the divide-by-8 circuit producing PHI/8 is shown to be the circuitry contained in the block 851, a psendo-randon shift counter clocked on the internal clock (H phases) of FIG. 4. The output signal 0/8 on line 26k becomes active after 8 internal clock phases have occurred. Note that for the circuitry contained in block 851 to produce .0./8, the start signal from the circuitry contained in FIG. 18b must be active. The other source of clock input is the external clock marked "ECC" input through device 850. The complex gate circuitry 849 determines which of these two clock sources 26k or ECC will be the single clock source for the timer circuitry; this is done by examining the TM and TM signals from the timer control register P3. If the bit 6 of the timer control register is "2", then the external clock source EC obtained from the 7th bit of port A is used, otherwise the signal .0./8 on line 26k is used as a clock source. The clock source 26m is then input into NOR gate 847 which also receives inputs from the start/stop bit -7 of the timer control register P3 and the timer output 21j. This signal is further clocked by H2 in device 846 and used as the decrement signal PDECH2 input on line 26u into the circuitry contained in FIG. 18b. The output of the clock circuit PCOUT in FIG. 18b, on line 26p, is transformed into the signal PLTVH2 through the circuitry 844 combining it with a start signal and through device 845 which clocks PLTVH2 by the clock phase H2 and then transmits the signal via line 26q into the circuitry illustrated in FIG. 18b.

PMDTLH4 on a line 26r produced by circuitry in FIG. 18a that is also input into FIG. 18b and will be discussed; this signal causes a write into P3 or address 0103. The output of the prescaler circuitry PCOUT is also used as an input through inverter 843 into the latch circuitry 842. This latch circuitry and its gate input is used to generate and latch the interrupt 2 flag at 842a which is a function of PCOUT, the timer generate and output and the clock phase H2.

The PCOUT signal is also used to construct TDECH2 at line 26a, FIG. 18a. This uses PCOUT after inverter 848 and is input into a NOR gate 841 which receives inputs from the stop line 26t, start line 26u and TCOUT line 26v and further clocked by H2 through device 840. TDECH2, line 26s, is the decrement command for the timer value register 26. TLTVH2 (load timer value) on line 26w is also produced by PCOUT from inverter 843 combined with TCOUT (output 26v of the timer) and the quantity ANDed, NORed with the start line 26u in the complex gate circuitry 838, and then further clocked by H2 in device 839. Memory data bus MD access to the timer control register and timer data registers P2 and P3 are provided by lines PMDTLH4, TVTMDH4, TCTMDH4, and TMDTLH4 generated in the circuitry of FIG. 18a. PMDTLH4 results from NOR gate 832 receiving the enable input GTP derived from the group decode circuitry 27, LNGWR input through inverter 835 from the memory control circuitry 28, and BAO from the memory control circuitry 28. This signal from 832 is then clocked by H4 through buffer 833 and input into the circuitry illustrated in FIG. 18b via line 26r. The purpose of this signal is to provide the write access into the timer control register P3. TVTMDH4 on line 26x provides the read capability for the timer data latch register P2, 0102, or the capability to read the current timer value, and is generated by devices 830 and 831 which work in the same way as devices 832 and 833. Likewise, TCTMDH4 on line 26y from devices 828 and 829 provide a read capability for the timer capture register P3. TMDTLH4 on line 26z from devices 826 and 827 likewise provides the write enable signal for the timer data latch register P2, allowing the user to write from the MD bus the latch value into the timer data latch register. TVTCH2 is an input to the FIG. 18c circuitry from the interrupt logic circuitry that provides the interrupt 3 input to activate 26c for the event latch timer mode.

In FIGS. 18b and 18c, each register bit for the timer contains two inverters and a feedback transistor like 15i and 15j of FIG. 7b; the timer registers are part of the strip with the eight metal lines of the MD bus running vertically and the control lines 26q 26s and 26v-26z running horizontally.

The circuitry contained in FIG. 18b is the circuitry representative of the write function of the timer control register P3 illustrated in FIG. 18e. That is, bits 0-4 represent the value input into the prescale latch 26a-1. Bit-5 is always a "0"; or unused; therefore there is no circuitry provided. Bit-6 specifies the source for the timer, i.e., internal clock or external clock; and bit-7 is the start/stop bit for timer control. Circuitry block 726-0 contains the circuitry to read the prescale value latch data being input into the prescale latch. This data when read in from the memory bus through MDO is loaded into a bit latch circuitry consisting of inverters 728, 729 and timing device 730, labelled PLO. This input is made through device 727 which becomes active when a write operation is performed as activating PMDTLH4 previously discussed. This value is then input into the prescale latch value register PV0 consisting of inverters 733, 734 and timing device 735 further controlled by device 731 which is active when PLTVH2 becomes active. PLTVH2 becomes active when either a start signal is received (a "1" in bit 7 of the control register) or the prescale latch value register is decremented below "0". During the normal timing sequence, the contents of the prescaler value register PVO, is decremented by device 737 and 739 together with the gating device which is activated by PDECH2. In addition, the value through inverter 737 is input into the next column of circuitry 726-1. The circuitry in 726-1 is similar to that in 726-2, 726-3 and 726-4. Therefore only the circuitry in 726-4 will be discussed.

The input from the memory data bus for 726-4, MD4, is stored in the prescaler bit latch PL4 similar to PLO in 726-0. Likewise, the value written is then stored in the prescaler value register section PV4 in a manner similar to PVO. A difference from circuitry 726-0 and 726-4 is the existance of the devices 722, 723 and 724 and in addition 725 in 726-3, 726-2 and 726-1. These devices provide for the decrementing and restorage of the value in the prescaler value register and for the prescaler output on line PCOUT when the contents of the prescaler value register is decremented below "0" as previously discussed. It should be noted FIG. 18b only contains the circuitry for the timer control register write state and not the timer control register read state consisting of the event latch value.

The timer data latch, the actual timer value and the capture latch value are contained in the circuitry as shown in FIG. 18c. These three registers are similar in circuitry to the registers in the prescale value register and prescale latch in FIG. 18b. Specifically the timer latch register is signified by TL7, through TL0 in FIG. 18c. TLO consists of two inverters, 764, 765 and a timing device 766 which operates as a master/slave latch similar to the prescale circuitry previously discussed. The timer latch value is written into this bit position during the activation of device 763 which is activated by the signal TMDTLH4 as previously discussed. Therefore, when TMDTLH4 is active, the latter latch value is written into the timer latch registers or the timer latch register cells TL7-TL0. The contents of the timer latch is then input into the timer value register TV7-TV0. TV0 contains the inverters 774, 775 and timing device 776 operating as a master/slave bit latch. The timer value is input upon the occurence of TLTVH2 which is produced when either the prescale circuitry output PCOUT and when the timer outputs PCOUT, or when the start signal is active as previously discussed. Therefore when this line becomes active, the value in the timer latch register TL7-TL0 is loaded into the timer value register TV7-TV0. Located in between the timer value register and the timer latch register in FIG. 18c is the event latch register. In section 738-0 the event latch register bit is stored in the master/slave bit latch circuitry containing inverters 769, 770 and timing device 771. It should be noted that the contents of this master/slave latch can be read when TCTMDH4 becomes active, i.e., device 772 becomes active allowing the master/slave circuitry to activate device 768. In addition, the input from the interrupt logic circuitry signifying the occurrence of interrupt 3 (TVTCH2) is used to update the capture latch register with current timer value. The circuitry used to decrement the contents of the timer value register (TV7-TV0) is similar to that used to decrement the prescaler value shown in FIG. 18b. Specifically inverters 780 and 782 and timing device 781 in circuit segment 738-0 is similar to the inverters 737, 739 and timing device 738 and circuit segment 726 in FIG. 18b. The actual decrementing occurs when the device 781 and similar devices and circuit segments 783-7 - 783-1 becomes active; this occurs when TDECH2 is active. When the contents of the timer value register passes through a "0", TCOUT becomes active which produces the interrupt 2 flag through latch 842 in FIG. 18a as previously discussed.

INPUT/OUTPUT PORTS

The processor system includes four 8 bit input/output (I/O) ports, A, B, C, and D. These I/O ports can be reconfigured for each of the different processor modes; single chip mode, peripheral expansion mode, full expansion mode, microprocessor mode, and emulator mode as explained in reference to FIGS. 2 and 13. The I/O configuration during initialization is reset to the single chip mode with four external I/O ports. While two most significant bits in the I/O control register must be "0"s to select the single chip mode, these bits are automatically cleared during reset. There are four 8 bits I/O ports as shown in FIG. 2a and FIG. 1 for the single chip mode. All four ports are located in the peripheral file PF, addresses 01XX, tied to the MD bus, and may thus be manipulated efficiently with the I/O manipulation instructions of Table A. Referring now to FIG. 1, port A is an input 8 bit port with high impedance inputs. Port B is an 8 bit output only port. When port B is read, the value at the I/O pin is being read. Port C and D are 8-bit bidirectional data ports in which each bit can be individually programmed to be input or output. Associated with each bidirectional port is a data register such as P8 or P10 and a data directional register such as P9 or P11. Each I/O bit line can be programmed to be an input or output by setting a "1" in the corresponding data direction register for those lines which are to be outputs. A "0" in a bit of the data direction causes the corresponding I/O line to be a high impedance input. The data register P4,P6,P8,P10 is used to read and write the I/O lines. A "1" in the data register will cause a high on the I/O line if it is programmed as an output.

When the processor is in the peripheral expansion mode, I/O port C and bits 4-7 of I/O port B are used for the memory expansion. Port A, Port D and bits 0-3 of Port B are not affected. Specifically port C bits 0-7 and port B bits 4-7 are used for the external memory interface. The I/O lines of port C 0-7 are used to pass multiplex address/data as shown in FIG. 13a. Output lines of port B bits 4-7 are used for memory interface timing and control as shown in FIG. 13a. The peripheral expansion mode memory map is shown in FIG. 2b.

In the full expansion memory mode, the I/O port C, port D and bits 4-7 of port B are used for the memory expansion. Port A and bits 0-3 of port B are not affected. I/O port C bits 0-7, port D bits 0-7, and port B bits 4-7 are used for external memory interface. I/O port D bits 0-7 are used to pass the most significant byte of the 16 bit address. I/O port C bits 0-7 are used to pass the least significant byte multiplexed address and data as shown in FIG. 13b. The output lines for port B bits 4 7 are used for memory interface timing and control. The full expansion mode memory map is shown in FIG. 2c.

The I/O configuration for the microprocessor mode is the same as the I/O configuration for the full expansion mode. The processor is placed in the microprocessor mode when the MC pin is tied to Vcc. The microprocessor mode is identical to the full expansion mode, except that the internal on-chip ROM 11 is disabled and removed from the memory map of FIG. 2d. The revised memory map is shown in FIG. 2d.

The emulator mode is enabled when the MC pin is tied to a high voltage source (+12 volts). In the emulator mode, all on-chip I/O and ROM is disabled and removed from the memory map as shown in FIG. 2e. The emulator memory expansion interface operates identical to the microprocessor mode memory map interface with the exception of the memory map and the pin-out. Specifically, in the emulator mode, all internal peripheral files (Ports A, B, C, D, timer, I/O control register, ROM) are disabled. Port B bits 7-4 become external memory control outputs. Port B bit 3 serves as an output for INTA, the external interrupt acknowledge. Port C and port D are configured in the same manner as in the microprocessor or full expansion modes. The emulator mode can support up to 128 interrupts, either maskable or nonmaskable. When the interrupt acknowledge INTA line goes low, the external I/O circuitry must place the appropriate interrupt vector on the data bus. The interrupt vector transfer is independent of the other memory control signals. The interrupt vector is used to form the lower order bit of the memory address which contains the low order bit of the interrupt service routine entry point. The entry point vector is multiplied by 2 to obtain the address bit. Hex FF is the high order byte of the memory address which contains the entry point address least significant bit. The entry point address least significant bit is stored adjacent to the most significant bit. It should be noted that the interrupt vector values are equivalent to the trap opcodes. Thus the interrupt vector corresponding to interrupt 2 is hex FD as before.

The I/O Port A functions as an input port for the single chip mode, the partial expansion mode, the full expansion mode and the microprocessor mode. During the emulator mode, port A is disabled by the group decode circuitry as previously described.

Referring now to FIG. 19a, 7 bits of information are obtained from the seven pads of the "A Port" (bits 6-0). Actually there is a separate line of circuitry and pad for each separate bit that are identical to the one shown in FIG. 19a. For these 7 bits the signal is transmitted through standard input protection circuitry A-1 and through a device A-2 clocked by H2 and through dual inverters 210 and device 211 activated from the A port enable signal GA generated in the group decode circuitry 27, FIG. 16b. It should be noted that the A port enable GA signal is clocked through device 214 by H2 and transmitted through inverter 215 into a driver 216 clocked by H4. Bit 7 of A port is different from bits 0-6 and serves two purposes. The first purpose is merely as the 8th bit of information input just as bits 0-6 and thus is transmitted through similar circuitry, gated by H2, transmitted through inverters 212 and controlled by the A port enable signal GA from the group decode circuitry as in A port bits 6-0. In addition the bit 7 may be used as the event counter input (ECC) transmitted to the timer circuitry (see FIG. 18a). To this end, the event counter signal from A7 is transmitted through inverters 217 and further clocked by H1 and H2 into circuitry 218 which latches the occurrence of the event before it is further clocked by H4 through the NOR gate circuitry 219 to the timer FIG. 18a.

In the single chip mode, I/O port B serves as an 8 bit output port. In the partial expansion mode, the full expansion mode and microprocessor mode four bits of port B are external memory controls (CLOCKOUT, ENABLE, RD/WR and ALATCH). In the emulator mode port B bits 7-4 are external memory controls as before but bit 3 serves as an output for INTA, the external interrupt acknowledge line. In these modes (all modes but the emulator mode) where the 4 bits are used for external memory controls, the other 4 bits are unused. If it is desired to emulate an 8-bit output port, circuitry has been included that allows the user to make use of the four unused bits of port B in combination with 4 bits built externally see FIG. 13b or c. To output from port B, a port B address is output on port C (or port C and D depending on the mode) and external hardware places MD (3-0) or the bits 0-3 of the memory data bus into the port B bits 3-0 latches and onto the port B pads. The hardware further allows port C to output from the memory data bus bits 7-4 into the external 4 bits of port B (7-4). Bits 0-3 of the memory data bus, MD (3-0) is also output from port C, but are not used externally if the 4 internal B port bits are used. It should be noted that the data output on port B is latch data and thus can be read. To read port B the port B address is sent out to port C and hardware allows only the external port B bits 3-0 or the contents of their data latch to be read onto the memory bus, MD (3-0) and allows only port C bits 7-4 to be read from the external port B onto the memory data bus, MD (7-4).

Referring now to FIG. 19b, the pads for the B port bits 7-4 are shown and the associated circuitry is identical for each individual bit pad. The difference is for the circuitry structure 211. The one of the four control lines are input into the NAND gate in the circuit structure 221 according to which bit position. The bit 7 input is the clock or phase H3, the bit 6 input is the enable line, the bit 5 input is the read/write signal (BWRB) and the bit 4 input is the ALATCH signal. MD (7-4), is clocked through device 224 by the port B write signal clocked by BWRH4. This line is then transmitted through the circuitry 220 as previously discussed which also includes the reset signal (RESET) for clearing the latch and then into complex gate 221 where it is combined with the single chip mode signal line, SCR, and the respective control line and through device 222 onto the pad for the respective bit. Also, the input can be taken from this bit pad through standard input protection through a device clocked by H2 and inverter and a NOR gate 223 which also receives an input from the single chip mode line. This input can then be read onto the memory bus as shown.

Bit 3 originates from the memory data bus line marked "MD3" through a gating device 226 which is gated by the read/write line originating from the circuitry below in FIG. 19b through a series of gating devices and inverter NAND gate 225 which serves the purpose to gate the output by H2 or during a reset operation to change the gate to an input mode. For the output mode, the signal is then transmitted to the gate circuit 227 which receives inputs from the INTAX signal used during the emulator mode as a interrupt acknowledge and also the emulator mode signal EM. Since B3 serves this external acknowledge purpose in the emulator mode, the output from this complex gate 227 is then transmitted through device 228 onto the bit 3 pad. The input from the bit 3 pad is transmitted through the input protection circuitry, clocked by H2 through an inverter, then into a NOR gate 229 which also receives an input from the emulator mode in order to disable the input line during the emulator mode. The bits 2 to 0 of the data bus are input through a gating device 230 which is gated by BWRH4 from the circuitry contained below and through the circuitry 231 which clocks the output onto the respective pads and resets the port to input during a reset condition. The output signal during the output mode is then transmitted through device 232 onto the respective pad. The input from the respective pad is transmitted through the input protection circuitry as before, and gated by H2 through two inverters onto the memory data bus lines for bits 20 marked MD (2-0) and clocked by BRDH4. Note that SCR is the OR of the SC and the reset signal from the interrupt logic circuitry illustrated in FIG. 17a. GB and LNGWR are the B port enable line and read/write line from the memory control circuitry illustrated in FIG. 16c. GB is clocked by H2 and is an input to NOR gate 233 along with LNGWR which is then transmitted through device 235 clocked by H4 to produce the output or write signal BWRH4. In a similar manner, the GBP signal is input into NOR gate 234 together with the inverted LNGWR signal (BWRB) and then transmitted through device 236 clocked by H4 to produce the input or read signal BRDH4.

In the single chip mode, port C is an 8 bit I/O port with one address for data and one address for port direction. In other words, setting a bit in a port direction will determine whether that bit in port C is in input bit or an output bit. Specifically, setting the direction latch to "1" sets the correponding bit position of the port into an output mode. The signals CDATAOUT from the memory control circuitry illustrated in FIG. 16c enables port C to output an adress in the first state of a long read or write cycle and then if in an output mode, allows port C to output the contents of the data latch onto the port C bit pads.

Referring to FIG. 19c, the data from the memory bus, MD (7-0), is clocked through device 237 into the data latch circuitry 238. The data is then transmitted through the complex gate circuitry 239. Note that the circuitry 239 also receives the address, BADD (7-0), from the address bus together with the CDATAOUT signal from the memory control circuitry as previously mentioned. This data (or address) is then transmitted over the line marked CDATAB (7-0) to device 240 which also receives an enabling signal CHIZ. The enabled output is then transmitted to the C port pads. CHIZ originates from a circuitry containing a direction latch. The direction latch inputs originate from the memory bus on lines MD (7-0) clocked through gate 241 by COWRH4 into the direction latch circuitry 242. Note that the direction latch circuitry also receives the reset signal from the interrupt circuitry in FIG. 17a. This reset signal resets the data latch for each bit to the input mode as previously explained. The output of the data latch is DIRC (7-0). The reset signal also is input into the complex circuitry 243 together with DIRD (7-0) from circuitry 242. Complex circuitry 243 also receives PTCOUT and SC. SC is the signal for the single chip mode and during the single chip mode PCOUT is disabled allowing the contents of the direction latch to determine the port direction. PTCOUT is enabled and places port C into an output mode in both states of a long write cycle and input mode in the first state of a long read cycle. PTCOUT originates from the memory control circuitry illustrated in FIG. 16c. Inputs from port C originate on the pad for the respective bits 7-0 and are transmitted through the input protection circuitry through a device clocked by H2 and an inverter into complex gate 244. The input data CPADP (7-0) is gated with DIRC (7-0) from the directional latch 242 and is read through device 246 onto the memory bus MD (7-0) clocked in by CERDH4 through device 247. Also the same line to the memory data MD bus can be used to write the data contained in the port C latch 238 which has been gated with the directional latch 242. This enables the user to read the data that is being output or stored in the output latch. The devices 248 and 249 are clocked by a signal EXTRDH4 which is used in any nonsingle-chip mode to read the C port pads onto the memory data bus in state 2 of a long memory read cycle if a valid external address is provided. However, if port B address is provided, the port B enable signal GB is active and does not allow the bits 3-0 of Port C to be read onto the MD bus via NOR gate 250. These 4 bits are contained in the internal B port and read onto the memory data bus MD (3-0) as previously discussed. The EXTRDH4 signal is produced by the inputs from the memory control circuitry including SC, single chip mode, EXTC signifying an external operation, and LNGWR for the read/write operations. These signals are combined in NOR gate 251 and then clocked by H4 in device 252. CEWRH4 is the output signal for the data and is used to clock device 237 to transfer data from the memory data bus into the port C data latch 238. This signal originates from complex gate 253 which receives inputs from the single chip signal signifying a single chip mode and from the port C enable signal from the group decode circuitry (FIG. 16b), GC, BAO from the memory control circuitry illustrated in (FIG. 16c) signifying a data operation and LNGWR from the memory control circuitry in (FIG. 16c) signifying a write operation. The signal from 253 is then transmitted through device 254 clocked by H4. The directional or control information is written into the directional latch 242 through device 241 clocked by COWRH4, COWRH4 originates from NOR gate 255 which receives inputs from the decoder circuitry in a form of GCP, BA indicating a write operation into this latch, and LNGWR signifying a write operation. The output from gate 255 is transmitted through device 256 clocked by H4. CERDH4 is the signal that enables the input data from port C to be input on the memory data bus, MD (7-0) through device 247 and originates from NOR gate 257 which receives inputs from GCP, BA, and BWR which is the negated LNGWR signifying a read operation. The output of gate 258 is then transmitted through device 257, clocked by H4. CORDH4 is used to input the contents of the direction register 242 through device 245 onto the memory data bus MD (7-0) and originates from NOR gate 259 which receives inputs of GC, BAO and BWR. The output of gate 259 is transmitted through device 260 clocked by H4.

In the single chip mode, port D is similar to port C in that it is a bidirectional I/O port that contains a directional latch and a "1" set in the latch for a corresponding bit the output mode. In a peripheral expansion mode, port D is the same as the single chip mode. However, in the microprocessor mode full expansion mode and emulator mode, port D serves as a 8 bit high address output.

Referring now to FIG. 19d, if port D is in the output mode, the output information is obtained from the memory data bus MD (7-0) and transmitted through device 261 clocked by signal DEWRH4. This information is transmitted through the data latch 262 into complex circuitry 263. The complex circuitry 263 also receives inputs from the data bus address line BADD (F-8) and DADDOUT which allows port D to output the high address, BADD (F-8), during the emulator mode, microprocessor mode and full expansion mode. The output from complex gate 263 is then transmitted through device 264 onto the D port pads. Similar circuitry exists for each of the 8 pads. Device 264 is disabled when that bit position is in the input mode determined by the direction latch 266. The contents of the direction latch for each of the bit positions is read from the memory bus MD (7-0) gated by DQWRH4 in device 265 into the direction latch 266. The output of the direction latch is transmitted into complex gate 267 which is combined with the reset signal also input into the directional latch together with the DADOUT signal previously discussed. The output of complex gate 267 is DHIZ which is the disabling signal for the device 264. Two sets of information can be read from port D. The actual data input from the port pad and the contents of the direction latch. The contents of the direction latch is output by the line marked DIRDB (7-0) through a device 268 gated by DORDH4. The input from the D port pads is transmitted through the input protection circuitry clocked by H2 and through an inverter into complex circuitry 270 which also receives the contents of the directional latch. This enables the user to read the input from the pad or the information contained in the output data latch 262 determined by the information for that bit contained in the direction latch. The output of this complex gate is then transmitted through device 271 and through device 269 clocked by the signal DERDH4 onto the memory data bus. The signal DEWRH4 (write data into data latch) used to gate device 261 is produced in NOR gate 272 from the enable D port signal, GDP, LNGWR0 and BAO, all from the memory control circuitry illustrated in FIGS. 16b and 16c. BAO signifies a write operation into the latches contained in port D. LNGWR signifies a write operation or output operation from port D. The output from gate 272 is transmitted through device 273 clocked by H4. DOWRH4 is the signal to enable device 265 to enable the user to write into the direction latch 266 and is produced in NOR gate 274 from signals GDP, BAO and LNGWR. The output of NOR gate 274 is transmitted through device 275 clocked by H4. DORDH4 is used to enable the output of the contents of the direction latch onto the memory bus and is produced in NOR gate 276 from the signal GDP, BWR from port C and BAO. The output of NOR gate 276 is transmitted through device 277 clocked by H4. DERDH4 is the signal used to clock device 269 to allow the output of either the contents of the port D data latch 262 or the inputs from the port D input pad and originates from NOR gate 278 which has signals GDP, BAO, and BWR. The output of gate 278 is transmitted through device 279 which is clocked by H4.

The buffers 222, 228, 232 for the B port may be conventional MOS output buffers, while the buffers 240 and 262 for the C and D ports may be conventional tri-state MOS output buffers.

Keyboard and Display Scan Program

An example of a program executed in the microcomputer 10 connected to a system of FIG. 13a is listed in Table J and shown in flow chart form in FIGS. 20a and 20b. The keyboard input part of the program could be used in the FIG. 13b-13d systems. The microcomputer 10 having features of the invention permits keyboard and display functions under control of the fixed program in the ROM 11 rather than requiring external control circuitry. The method implemented in the program uses time-multiplexing of the display 13-1 and scanning the keyboard 13-2 with the digit-actuating B-port signals as disclosed in U.S. Pat. No. 4,074,351, assigned to Texas Instruments. In this example, a single-pole push button keyboard 13-2 with twenty keys and an eight-character LED display 13-1 are used; the program can be modified to handle up to a sixty-four single-pole keyboard and sixteen character display (using D port) with minimal changes, mostly in the intiallization subroutine INIT. However, the example program uses only the twenty keys shown in FIG. 20c, so only five of the B port bits (B3-B7) and four of the A port bits (A4-A7) are used in keyboard scan. The other three B port bits (B0-B2) actuate digits of the display but not the keyboard. The asterisk key (*) is referred to in the program as "FUN" or function key.

The format of Table J includes the ROM 11 address on the left, followed by the object code in hex, then the source statement using the macroinstruction mneumonics of Table A with accompanying operands, plus comments on the operation performed. This program listed in Table J is used with a background program which would occupy the remainder of the ROM 11. The keyboard and display scan program of Table J uses only about 225 bytes of the ROM 11, particularly addresses F800 to F8EB including look-up tables, so about 1800 bytes remain for the background program. Definitions of terms used in the table J program are given in Table K.

The initiallization routine INIT at F800 to F81E is executed during the power-up or reset operations and does not form part of the display and key scan functions implemented repeatedly by the Table J program. The background program operates with a hardware timer interrupt which used the timer 26 in the peripheral file PF to generate INT2 interrupts at a fixed rate to insure that the display routine is called often enough so that the display characters 13-1 do not flicker. The timer P2 is set to decimal "208" and the prescaler P3 set to "3", for the internal clock mode, by the instructions MOVP %D0, P2 and MOVP %C3, P3 at F810 and F813 in the INIT routine. This setting generates an INT2 interrupt about once every millisec when the timer increments to zero; each INT2 causes the program counter PCL, PCH to be loaded with the timer interrupt vector located at FFFA and FFFB, invoking the timer interrupt routine TINTR at F859, saving A and B in the stack and leading into the display/keyscan routine, MUXSCN at F85B.

After INIT, the program as seen in FIG. 20a enters a loop at F81F to F823 which continuously checks to see if the keyscan routine has left a new debounced key entry in DEBKEY, R119. This is done by writing hex 80 or 10000000 into B register and exchanging B with DEBKEY, then a bit test of 80 and B to see if they are the same; if not jump back to F81F, "KYDD". If a new keystroke has been loaded into DEBKEY, the instruction at F829 checks to see if it is the function key, and if so the instructions at F832 to F847 are executed to show the function symbol on the display for two seconds, then return to the F81C loop to wait for the next keystroke. If the keystroke is not the function key, F82F is executed, calling the STRSEG subroutine at F849-F858 which enters the segment pattern for this key (obtained from look-up table at F8DF) into the right most digit of SARRAY-1 and moves other digits one place to the left. At F858 RETS, execution returns to F81C to enter the loop to wait for the next key.

During the execution of the program of FIG. 20a, the occurance of the interrupt INT2 at counter time-out causes execution to shift to the timer interrupt routine of FIG. 20b. This routine is listed at F859 to F8CA of Table J, and begins with saving the A and B registers then ends with restoring these registers before the return instruction F8CA RETS; the PUSH and POP instructions implement this function.

In the TINTR part of the program, the chip 10 enables only one character of the display 13-1 at a time (one bit of B port), by the MOVP A, .P6 instruction at F868, beginning with the left-most or 0 character. At the point, the appropriate segment lines for that character location are energized by loading the port C register 010A with a segment pattern obtained from a look-up table; this is performed by the MOVP A, .P8 instruction at F863. A switch closure is detected at one bit of port A by the MOVP .P4,A instruction at F86A. If no key is down in that column, detected at F871, the remaining columns are examined via the loop of F871, F888, F8A7, F8AB and back to F86A, as seen in FIG. 20b. If the function key is down and debounced as detected at F879, the function flag is set at F87C and the remaining columns looked at via the path through F8A7 at F86A as before. For keys other than the function key the path via F881 tests for debounce, and if so the location of the down key is stored by F8A4 to be then used in the main program.

Debounce is used to eliminate effects of transients when a key is pushed. When a key is detected, it is not acted upon unless it appears for the number of scans defined by DEBNCE, in this case four, stored in the function count register (FCNT) R127 or successive-read register (SUCCRD) R121. Whenever a key is detected but the number of successive detections is less than four, the register R121 or R127, as the case may be, is decremented (count is incremented) and the scan resumed via F879 or F8A1. Thus, a key must be down for about four milliseconds before an indication of its presence is passed back to the main program.

The program of Table J and FIG. 20a, 20b merely scans the keyboard and displays what is entered. The operations performed on the functional commands and numbers entered are not included. These could be included in the loops of FIG. 20a, such as at F830. That is, the D port inputs could be scanned and/or outputs energized as in FIG. 13a; also, other interrupts INT1 and INT3 could be processed.

The Self-Test Procedure

A microcomputer 10 constructed according to the invention may contain a self-test procedure as set forth in U.S. Pat. No. 4,158,431 issued to Van Bavel et al, assigned to Texas Instruments. The procedure of U.S. Pat. No. 4,158,431 consists of exercizing all of the display characters 13-1 and keys 13-2 as well as all of the I/O devices on the D port of FIG. 13a, all under control of a sequence of macroinstructions in the ROM 11 as manufactured. This self-test procedure establishes that all of the external elements of the system are working and gives some indication that the chip 10 itself is fully functional, but this is not an exhaustive check. Prior to connecting into such a system, however, functional testing must be done. For example, to test the contents of the ROM 11 after manufacture (either prior to delivery to the customer or by the customer as incoming material inspection) it has previously been the practice to read out the entire contents of the ROM, one word at a time, and compare each word with the desired bit pattern. Microcomputer devices which allow such testing are disclosed and claimed in U.S. Pat. No. 3,921,142 issued to John D. Bryant et al and U.S. Pat. No. 4,024,386 issued to E. R. Caudel and Joseph H. Raymond, both assigned to Texas Instruments. Such tests, however, require that the test machine store the entire ROM code, 2048 or 4096 bytes, and require a different check code for each different ROM code. Further, the check requires at least one transfer between test machine and device under test for each byte of the ROM. These factors make the test unduly long, require extensive test data or software, and/or use up excessive amounts of program space in the test machine.

The microcomputer 10 may employ a test method in which a two-byte macro-code is mixed in the ROM 11 upon manufacture and used to check the remaining macro-code. This two-byte code is different for each ROM code or program and represents some function of all of the other bytes coded in the ROM. For example, it might be the LSB's of the sum of all the other bits in the ROM, or preferably some other function which provides a multiple check of all bits. The two-byte code is referred to as a cyclic redundancy code or CRC and is a 16-bit value which is a function of every bit of data used to create it. The CRC is calculated using every byte of the macrocode in the ROM except the CRC itself which is stored at a location such as F802 and F803 in a 2048 bit ROM 11 or F002 and F003 in a 4096 bit ROM 11.

The program of Table L is loaded into the RAM 12 of the chip 10 while the chip is in the microprocessor mode (FIG. 2d) or in one of the expansion modes (FIGS. 2b or 2c), by a sequence of move double MOVD or move MOV instructions. For example, MOVD %7D02, R10 in the microprocessor mode places the first two bytes of the object code of Table L in RF locations R10, R11. In this manner, all of the code of Table L is stored in RAM 12, and then a MOV %00, P1 instruction returns the microcomputer 10 to the single-chip mode of FIG. 2a, with the address of R10 in the program counter PCL so execution of the Table L code begins. The two-byte address in ROM 11 being accessed for test is AL, AH (two of the RF registers, R125 and R124). The present calculation result is QL, QH (in R127, R126). The code at 0B and 1B merely checks to see if AL, AH is at the address of the CRC code in ROM 11 (F902 and F903, for example), if so AL, AH is incremented two bytes. The code at 1D to 2A checks to see if the AL, AH address has incremented past FF, in which event all of the ROM has been processed so a jump to the CHKDON sequence is executed; otherwise the pointer AL, AH is incremented and the main calculation BUILDF is executed. This calculation at 2D to 48 processes the current QH, QL value with the new byte in Reg B which was fetched from the AL, AH address, and produces a new QH, QL value. BUILDF ends in a jump to the LOOP starting at OB. After all bytes in ROM have been passed through BUILDF, the check is finished. The code at 4A to 4F then defines port C as an output and outputs a hex 55 (binary 01010101) to indicate to external that the calculation is finished, so the test machine is alerted to look for the 2-byte result on the C and D ports. The original code from F902, F903 is compared at 53 and 5E with the QH, QL value, and the comparison output. About 890,000 machine states are needed by the microprocessor 10 to execute this test program, but this is all internal; the test machine does not need to store unique codes and off-chip accesses are not needed for the bulk of the test.

Conclusion

The microcomputer described in detail herein is in the form of an N-channel silicon gate integrated circuit in a single silicon chip. However, features of the invention can be used in devices made by other processes such as metal gate, P-channel, CMOS, silicon-on-sapphire, and the like. Also, the memory 11 has been described as a ROM of the fixed-program type, but of course an electrically-programmable ROM or electrically-erasable ROM may be used. The ROM 11 is referred to as a program memory and the RAM 12 as a data memory, and these are the primary functions in many applications; it is understood, however, that "data" from the ROM 11 is used in some algorithms ("data" being numerical constants and the like), and that the device can execute instruction codes from the RAM 12, or program blocks can be down-loaded into RAM 12 from external tape or disc drive, or from a telephone coupler, for example, and executed from RAM 12. Furthermore, additional control lines and functions such as READY, HOLD, bus-status code, etc. as in said U.S. Pat. No. 4,402,044 may be used in a device having features of the invention.

While this invention has been described with reference to an illustrative embodiment, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiment, as well as those embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

TABLE A THE INSTRUCTION SET

ARITHMETIC INSTRUCTIONS

ADC: ADD WITH CARRY Opcode: 0XXX1001

Definition: Add the source operand to the destination operand (both from RAM 12) with carry-in and store the result at the destination address in RAM 12. Set status bit C to `1` on carry-out of (s)+(d)+C. Set N and Z on result. Application: ADC is used to implement multi-precision addition of signed or unsigned integers.

ADD: ADD Opcode: 0XXX1000

Definition: Add the source operand to the destination operand and store the result at the destination address in RAM 12. Set status bit C to `1` on carry-out of (s)+(d). Set N and Z on result. Applications: ADD is used to add two bytes, and may be used for signed two's complement or unsigned addition.

CMP: COMPARE Opcode: 0XXX1101

Definition: Subtract the source operand from the destination operand; do not store the result. Set status bit C to `1` if (d) is logically greater than or equal to (s). Set N to `1` if (d) is arithmetically less than (s). Set Z to `1` if (d) is equal to (s). Applications: CMP is used to compare the destination operand to the source operand. The N bit is set to `1` if (d) is less than (s), interpreting (d) and (s) as two's complement integers. The C bit is set to `1` if (d) is greater than or equal to (s), interpreting (d) and (s) as unsigned integers. For either signed or unsigned equal. The status bits are set upon the result of computing (d)-(s). N and Z are set on the result of this subtraction. The carry bit C is a "borrow" bit--i.e. it is `0` if (d) is logically less than (s). Negative numbers are considered arithmetically less than, but logically greater than, positive numbers. The CMP instruction can be used with the conditional branch instructions to branch on the comparison between the destination operand (D) and the source operand(S).

DAC: DECIMAL ADD WITH CARRY Opcode: 0XXX1110

Definition: Add the source operand to the destination operand with carry in and store the result at the destination address in RAM 12. Each operand is a two digit integer using BCD format. Set status bit C to `1` if value of (s)+(d)+C is equal to or greater than 100. Applications: DAC is used to add bytes in binary-coded decimal (BCD) form. Each byte is assumed to contain two BCD digits. Operation of DAC is undefined for non-BCD operands. DAC with an immediate operand of zero value is equivalent to a conditional increment of the destination operand. The DAC instruction automatically performs a decimal adjust of the binary sum of (s)+(d)+C. The carry bit is added to facilitate adding multi-byte BCD strings, and so the carry bit must be clearing before execution of the first DAC instruction.

DEC: DECREMENT Opcode: 1XXX0010

Definition: Subract one from a copy of the operand and store the result in the operand address. Set status bit C to `1` if (d) decrements from 00 to FF; `0` otherwise. N: set on result. Z: set on result.

DSB: DECIMAL SUBTRACT WITH BORROW Opcode: 0XXX1111

Definition: Subtract the source operand and borrow-in from the destination operand and store the result at the destination address. Each operand is a two digit integer using BCD format. Set status bit C to `1` if no borrow required, `0` if borrow required. Set N, Z on result. Applications: DSB is used for multiprecision decimal BCD subtraction. A DSB instruction with an immediate operand of zero value is equivalent to a conditional decrement of the destination operand. The carry status bit functions as a borrow bit, so if no borrow-in is required, the carry bit should be set to `1`. This can be accomplished by executing the SETC instruction.

INC: INCREMENT Opcode: 1XXX0011

Definition: ADD one to a copy of the operand and store the result at the operand address. Set status bits C to `1` if (d) incremented from FF to 00, `0` otherwise. Set N, Z on result.

SBB: SUBSTRACT WITH BORROW Opcode: 0XXX1011

Definition: Subtract the source operand and borrow-in from the destination operand and store the result at the destination address in RAM 12. Set status bits C to `1` if no borrow is required, `0` otherwise. Set N, Z on result. Applications: SBB is used for multiprecision two's complement subtract. A SBB instruction with an immediate operand of zero value is equivalent to a conditional decrement of the destination operand. With (s)=0, if C=`0`, then (d) is decremented, otherwise it is unchanged. A borrow is required if the result is negative, in this case, the carry bit is set to `0`.

SUB: SUBTRACT Opcode: 0XXX1010

Definition: Subtract the source operand from the destination operand and store the result at the destination address. Set status bit C to `1` if result equal to or greater than 0; `0` otherwise. Set N, Z on result. Applications: SUB is used for two's complement subtraction. The carry bit is set to `0` if a borrow is required, i.e. if the result is negative.

JUMP AND BRANCH INSTRUCTIONS

BTJO: BIT TEST AND JUMP IF ONE Opcode: 0XXX0110

Definition: Logically AND the source and destination operands and do not copy the result. If the result is non-zero, then perform a program counter relative jump using the offset operand. The program counter is set to the first byte AFTER the BTJO instruction before the offset is added. Set status bits to zero. Set Z, N on (s) AND (D). Applications: The BTJO instruction is used to test for at least one bit which has a corresponding one bit in each operand. For example, the source operand can be used as a bit mask to test for one bits in the destination address.

BTJZ: BIT TEST AND JUMP IF ZERO Opcode: 0XXX0111

Definition: Logically AND the source and the inverted destination operand; do not copy the result. If the result is not equal to zero, then perform a program counter relative jump using the offset operand. The program counter is incremented to the instruction after the BTJZ instruction before the offset is added. Set status bits to `0`. Set Z, N on (s) AND (NOT d). Applications: The BTJZ instruction is used to test for at least one zero bit in the destinition operand which has a corresponding one bit in the source operand.

BR: BRANCH Opcode: 1XXX1100

Definition: Branch directly to location specified by the 16-bit addressing mode. The effective address is obtained using any one of the three extended addressing modes. Set no status bits on direct and indirect addressing. For indexed addressing, C, N, Z set on addition of B and the low address byte.

DJNZ: DECREMENT REGISTER AND JUMP IF NON ZERO Opcode: 1XXX1010

Definition: Decrement the operand the copy result to operand address. If result is non-zero, then take relative jump. Set status bit C to `1` if (d) decrements from 00 to FF; `0` otherwise. Set Z, N on resulting (d). Applications: The DJNZ instruction is used for looping control.

JC (etc.): JUMP ON CONDITION Opcode: 11100XXX

Definition: If tested condition is true, PC+offset is loaded into PC. No status bits are affected. Execution Results: The following table lists each conditional jump instruction, and the condition in which it will cause a jump to the location specified in the operand field.

    ______________________________________                                         Condition for Jump                                                             (Status Bit Values)                                                            Mnemonic                                                                               Carry   Negative Zero  Instruction                                     ______________________________________                                         JC      1       x        x     Jump if Carry                                   JN      x       1        x     Jump if Negative                                JNC     0       x        x     Jump if No Carry                                JNZ     x       x        0     Jump if NonZero                                 JP      x       0        0     Jump if Positive                                JPZ     x       0        x     Jump if Positive or Zero                        JZ      x       x        1     Jump if Zero                                    ______________________________________                                    

Applications: The Jump on Condition instructions may be used after a CMP instruction to branch according to the relative values of the operands tested. After MOV, MOVP, LDA, or STA operations, a JZ or JNZ may be used to test if the value moved was equal to zero. JN and JPZ may be used in this case to test the sign bit of the value moved.

JMP: JUMP UNCONDITIONAL Opcode: 11100000

Definition: Jump unconditionally using program relative addressing. PC plus offset is loaded into PC. No status bits are affected. Target address is within -127 to +128.

LOAD AND MOVE INSTRUCTIONS

LDA: LOAD A REGISTER Opcode: 1XXX1010

Definition: Copy the contents of the source operand address to and A register; addressing modes include direct, indexed, and indirect. Set status bit C to `0`. Z, N are set on value loaded. Applications: The LDA instruction is used to read values stored in extended memory. The direct addressing provides an efficient means of directly accessing a variable in general memory. Indexed addressing provides an efficient table look-up capability. Indirect addressing allows the use of very large look-up tables and the use of multiple memory pointers since any pair of file registers can be used as the pointer. The `decrement register and jump if non-zero` instruction (DJNZ) can be used with either indexed or indirect addressing to create fast and efficient program loops or table searches.

LDSP: LOAD STACK POINTER Opcode: 00001101

Definition: Copy the contents of the B register to the stack pointer register. No status bits are affected. Applications: LDSP is used to initialize the stack pointer.

MOV: MOVE Opcodes: 0XX0010, 1110X000X

Definition: Copy the source operand to the destination operand address. Set status bit C to `0`. Z, N are set on value loaded. Applications: MOV is used to transfer values in the register file. Immediate values may be loaded into registers directly from the instruction.

STA: STORE A REGISTER Opcode: 10XX1011

Definition: Copy the contents of the A register to the operand address; addressing modes include direct, indexed, and indirect. Set status bits C to `0`. N, Z are set on value loaded. Application: The STA instruction is used to read values not stored in the register or peripheral files. The direct addressing provides an efficient means of directly accessing a variable in general memory. Indexed addressing provides an efficient table look-up capability for most applications. Indirect addressing allows the use of very large look-up tables and the use of multiple memory pointers since any pair of file registers can be used as the pointer. The `decrement register and jump if non-zero` instruction (DJNZ) can be used with either indexed or indirect addressing to create fast and efficient program loops or table searches.

STSP: STORE STACK POINTER Opcode: 00001001

Definition: Copy the contents of the stack pointer register to the B register. No status bits are affected. Applications: LDSP is used to save the stack pointer if required. This instruction can be used to test the stack size.

SWAP: NIBBLE SWAP Opcode: 1XXX0111

Definition: Swap the least significant nibble (4 bits) of the operand with the most significant nibble and copy the result to the operand address. The SWAP instruction is equivalent to four consecutive rotate left (RL) instructions with the carry status bit set equal to the least significant bit of the result. Set status bit C to Bit 0 of result. Z, N are set on result. Applications: SWAP is used to manipulate four bit operands, especially during packed BCD operations.

XCHB: EXCHANGE WITH B REGISTER Opcode: 11010110

Definition: Copy the operand to the B register and then copy the original operand value to the B register. Set status bit C to `0`. Z, N are set on original contents of B. Applications: XCHB is used to exchange a file register with the B register without going through an intermediate location. The XCHB instruction with the B register as the operand can be used to test the B register contents for sign and equality with zero, like TSTB instruction.

LOGICAL INSTRUCTIONS

AND: AND Opcode: 0XXX0011

Definition: Logically "and" the source operand to the destination operand and store the result at the destination address. Set status bit C to `0`. N, Z are set on result. Applications: AND is used to perform a logical AND of the two operands.

CLR: CLEAR Opcode: 1XXX0101

Definition: Replace the operand value with all zeroes. Set status bits C and N to `0`. Z is set to `1`. Applications: CLR is used to clear or initialize any file register including the A and B registers.

INV: INVERT Opcode: 1XXX0100

Definition: Invert or complement all bits in the operand. Set status bit C to `0`. N, Z are set on result. Applications: INV performs a logical "or" one's complement of the operand. A two's complement of the operand can be made by following the INV instruction with an increment (INC).

OR: OR Opcode: 0XXX0100

Definition: Logically "OR" the source operand to the destination operand and store the result at the destination address. Set status bits C to `0`. N, Z are set on result. Applications: OR is used to perform a logical Or of the two operands.

XOR: EXCLUSIVE OR Opcode: 0XXX0101

Definition: Logically "exclusive or" the source operand to the destination operand and store the result at the destination address. Set status bit C to `0`. N, Z are set on results. Applications: XOR is used to perform a bit wise exclusive OR of the operands. The XOR instruction can be used to complement a bit(s) in the destination operand.

ROTATES

RL: ROTATE LEFT Opcode: 1XXX1110

Definition: Shift the operand to the left one bit position and fill the least significant bit and the carry status bit with the value of the original most significant bit; copy the result to destination address. Set status bits C to Bit(7) of original operand. N, Z are set on result. Applications: An example of the RL instruction is: If the B register contains the value 93, then the RL instruction changes the contents of B to 27 and sets the carry status bits. Numbers are in hex.

RLC: ROTATE LEFT THROUGH CARRY Opcode: 1XXX1111

Definition: Shift the operand to the left one bit position and fill the least significant bit with the original value of the carry status bit; copy the result to the destination address. Move the original operand most significant bit to the carry status bit. Execution Results: Bit(n)→Bit(n+1); Carry→Bit (0); Bit(7)→Carry. Set status bit C to bit(7) of operand. N, Z are set on result. Applications: An example of the RLC instruction is: if the B register contains the value 93 and the carry status bit is a zero, then the RLC instruction changes the operand value to 26 and carry to one. Numbers are in hex.

RR: ROTATE RIGHT Opcode: 1XXX1100

Definition: Shift the operand to the right one bit position and fill the most significant bit and the carry status bit with the value of the original least significant bit; copy the result to operand address. Execution Results: Bit(n+1)→Bit(n); Bit(0)→carry also. Set status bit C to Bit(0) of operand. N, Z are set on result. Applications: An example of the RR instruction is: If the B register contains the value 93, then the RR instruction changes the contents of B to C9 and sets the carry status bit.

RRC: ROTATE RIGHT THROUGH CARRY Opcode: 1XXX1101

Definition: Shift the operand to the right one bit position and fill the most significant bit from the carry status bit. Fill the carry status bit with the value of the original least significant bit. Set status bit C to Bit(0) of operand. N, Z are set on result. Applications: An example of the RRC instruction is: If the B register contains the value 93 (hex) and the carry status bit is zero, then the RRC instruction changes the operand value to 49 (hex) and sets the carry status bit.

SUBROUTINE CALLS

CALL: CALL Opcode: 1XXX1110

Definition: Push the current PC on the stack and branch to the effective operand address. For Indirect and Direct addressing mode there is no effect on Status bits. For Indexed mode, C, N, Z are set on addition of B and low address byte. Applications: CALL is used to invoke a subroutine. The PUSH and POP instructions can be used to save, pass, or restore status or file register values.

RETS: RETURN FROM SUBROUTINE Opcode: 00001010

Definition: Pull the top two bytes from the stack and branch to the resulting 16-bit address. No status bits are affected. Applications: RETS is typically the last instruction in a subroutine. RETS results in a branch to the location immediately following the subroutine call instruction.

TRAP: SUBROUTINE TRAP Opcodes: 1111XXXX, 11101XXX

Definition: Push the current PC on the stack and branch to the subroutine using a 16-bit address stored in high memory. No status bits are affected. Application: TRAP is used to invoke a subroutine. The PUSH and POP instructions can be used to save, pass, or restore status or file register values. There are 24 TRAP vectors which correspond to TRAP 0 through TRAP 24. The TRAP vectors are stored in memory in preselected vector address ending in FFFF. TRAP 1, TRAP 2, and TRAP 3 correspond to the hardware-invoked interrupts 1, 2, and 3 respectively. The hardware-invoked interrupts, however, push the program counter and the status register before branching to the interrupt routine, while the TRAP instruction pushed only the program counter. TRAP 0 will branch to the same code executed for a system reset.

STACK INSTRUCTIONS

POP: POP FROM STACK Opcode: 1XXX1001

Definition: Remove the top entry from the stack and copy to the operand address. Decrement the stack pointer to point to the new top-of-stack entry. Set status bit to `0`. N, Z are set on value popped. Applications: The data stack can be used to save or to pass operands, especially during subroutines and interrupt service routines. The POP instruction pulls an operand from the stack.

PUSH: PUSH ON STACK Opcode: 1XXX1000

Definition: Increment the stack pointer and place the operand value on the stack as the new top-of-stack. Set staus bit C to `0`. N, Z are set on value pushed. Applications: The data stack can be used to save or to pass operands, especially during subroutines and interrupt service routines. The PUSH instruction places an operand on the stack.

CONTROL INSTRUCTIONS

CLRC: CLEAR CARRY Opcode: 10110110

Definition: Clear the carry status; the sign and zero flags are determined by the contents of the A register. Set status bit C to `0`. N, Z are set on value of A register. Applications: CLRC is used to clear the carry flag if required before an arithmetic or rotate instruction. Note that the logical and move instructions typically clear the carry status. The CLRC instruction is equivalent to the TSTA instruction.

DINT: DISABLE INTERRUPTS Opcode: 00000110

Definition: Clear the interrupt enable flag in the status thus disabling further interrupts. Set status bit I to `0`. C, N, Z are set to `0`. Applications: DINT is used to turn off all interrupts simultaneously. Since the interrupt enable flag is stored in the status register, the POP ST, LDST, and RETI instructions may reenable interrupts even though a DINT instruction has been executed. During the interrupt service, the interrupt enable bit is automatically cleared after the old status register value has been pushed onto the stack.

EINT: ENABLE INTERRUPTS Opcode: 00000101

Definition: Set the interrupt enable flag in the status thus enabling interrupts. Set status bit I to `1`. C, N, A set to `1`. Applications: EINT is used to turn on all enabled interrupts simultaneously. Since the interrupt enable flag is stored in the status register, the POP ST, LDST, and RETI instructions may disable interrupts even though a TINT instruction has been executed. During the interrupt service, the interrupt enable bit is automatically cleared after the old status register value has been pushed onto the stack. Thus, the EINT instruction must be included inside the interrupt service routine to permit nested or multilevel interrupts.

IDLE: IDLE UNTIL INTERRUPT Opcode: 00000001

Definition: Suspend further instruction execution until an interrupt or a reset occurs. No status bits are affected. Applications: IDLE is used to allow the program to suspend operation until either an interrupt or reset occurs. The programmer assures that the interrupt enable status bit (and individual interrupt enable bits in the I/O control register) are set before executing the IDLE instruction.

NOP: NO OPERATION Opcode: 00000000

Definition: Perform no operation. No status bits are affected. Execution results in PC+1 loaded into PC. Applications: NOP is a null instruction which can be used as a pad instruction.

RETI: RETURN FROM INTERRUPT Opcode: 00001011

Definition: Pull the top two bytes from the stack to form the return address, pull the status from the top of stack, and branch to the return address. No status bits are affected because ST register is loaded from stack. Applications: RETI is typically the last instruction in a interrupt service routine. RETI restores the status register to its state immediately before the interrupt occurred and branches back to the program at the instruction boundary where the interrupt occurred.

SETC: SET CARRY Opcode: 00000111

Definition: Set the carry and zero status flags and clear the sign status flag. Set status bit C to `1`. N is set to `0`. Z is set to `1`. Applications: SETC is used to set the carry flag if required before an arithmetic or rotate instruction.

TSTA: TEST A REGISTER Opcode: 10110000

Definition: Set the status bits on the value of the A register. Set status bit C to `0`. Z, N are set on value in A register. Applications: This instruction can be used to set the status bits according to the value in the A register. It is equivalent to the TSTA instruction. It may be used to clear the carry bit.

TSTB: TEST B REGISTER Opcode: 11000001

Definition: Set the status bits on the value of the B register. Set status bit C to `0`. Z, N are set on value in B register. Applications: This instruction can be used to set the status bits according to the value in the B register. It may be used to clear the carry bit.

PERIPHERAL FILE INSTRUCTIONS

BTJOP: BIT TEST AND JUMP IF ONE--PERIPHERAL Opcode: 10XX0110

Definition: Logically AND the source and destination operands and do not copy the result. If the result is non-zero, then perform a program counter relative jump using the offset operand. The program counter is set to the first byte AFTER the BTJO instruction before the offset is added. Set Status bit C to zero. Z, N are set on (s) AND (D). Application: The BTJOP instruction is used to test for at least one bit position which has a corresponding `1` in each operand. For example, the source operand can be used as a bit mask to test for one bits in the destination peripheral file register, i.e. test bit 0 of the input A port, and jump if it is a `1`.

BTJZP: BIT TEST AND JUMP IF ZERO--PERIPHERAL Opcode: 1000X0111

Definition: Logically AND the source and inverted destination operands, and do not copy the result. If the result is non-zero, then perform a program counter relative jump using the offset operand. The program counter is set to the first byte AFTER the BTJO instruction before the offset is added. Set status bit C to zero. Z, N are set on (s) AND (NOT D). Applications: Similar to STJOP.

ANDP: AND-PERIPHERAL Opcode: 10XX0011

Definition: Logically AND the source and the peripheral file register specified in the destination, and place the result in the PF register. The source may be the A or B registers, or an immediate value. Set status bit C to `0`. Z, N are set on result. Applications: ANDP may be used to clear an individual bit in the peripheral file. Thus, it may be used to set an individual output line to zero. This may be done with an ANDP instruction where the source is an immediate operand that serves as a mask field. For example, bit 5 of the I/O control register (PO) is cleared, thus disabling level 3 interrupts.

MOVP: MOVE TO/FROM PERIPHERAL Opcode: 10XX0010

Definition: Read or write data to the peripheral file. The destination is read before the source is written into it. Set status bits C to `0`. Z, N are set on value moved. Applications: MOVP is used to transfer values to and from the peripheral file. This may be used to input or output 8-bit quantities on the I/O ports. For examples, MOVP P6,A reads the data on input port B. The instruction MOVP B,P4 outputs the contents of the B register onto I/O port A. The peripheral file also contains control registers for the interrupt lines, the I/O ports, and the timer controls. A peripheral file port is read during ALL peripheral file instructions including output operations such as `MOV A, P1`. If this read is undesirable as a result of hardware concerns, then a STA instruction should be used, using the memorymapped address of the peripheral register.

ORP: OR-PERIPHERAL Opcode: 10XX0100

Definition: Logically OR the source operand to the destination peripheral file register and write the result to the peripheral file register. The source may be the A or B registers, or an immediate value. Set status bit C to `0`. N, Z are set on result. Applications: ORP is used to perform a logical OR of the source operand with a peripheral file location, and write the result back to the peripheral file. May be used, to set an individual bit in the I/O control register, for example.

XORP: EXCLUSIVE-OR PERIPHERAL FILE Opcode: 10XX0101

Definition: Logically exclusive-or the source operand to the peripheral file register specified, and write the result to the peripheral file register. Execution Results: (s) XOR (d)→(d). Set status bit C to `0`. N, Z are set on result. Applications: XORP is used to perform a bit-wise exclusive OR of the operand. The XORP instruction can be used to complement a bit(s) in the destination PF register. For example, invert bit 0 of P9, which is the port C data direction register, thus reversing the direction of the bit.

                  TABLE B                                                          ______________________________________                                         MICROINSTRUCTIONS                                                              CROM 17 ADDRESS                                                                              MICRO-                  MICRO-                                                 INSTRUC-                INSTRUC-                                 HEX  BINARY   TION       HEX   BINARY TION                                     ______________________________________                                         00   00000000 IAQ-0      30    00110000                                                                              DAC-1                                    01   00000001 IDLE-0     31    00110001                                                                              MOVD-1                                   02   00000010 INT-2      32    00110010                                                                              RESET-2                                  03   00000011 INT-4      33    00110011                                                                              MOVD-2                                   04   00000100 MPY-1      34    00110100                                                                              MPY-7                                    05   00000101 EINT-0     35    00110101                                                                              MPY-6                                    06   00000110 DINT-0     36    00110100                                                                              IAQ-1                                    07   00000111 SetC-0     37    00110101                                                                              MOVD-3                                   08   00001000 POPST-0    38    00110000                                                                              IDLE-1                                   09   00001001 STSP-0     39    00110001                                                                              INT-3                                    0A   00001010 RETS-0     3A    00111010                                                                              RETS-2                                   0B   00001011 RETI-0     3B    00111011                                                                              RETI-2                                   0C   00001100 TGA-6      3C    00111000                                                                              DSB-1                                    0D   00001101 LDSP-0     3D    00111101                                                                              BtoPPL-3*.sup.(3)                        0E   00001110 PushST-0   3E    00111110                                                                              RJMP-4                                   0F   00001111 LDST-0     3F    00111111                                                                              RJMP-5                                   10   00010000 MOVD-4     40    01000000                                                                              DecD-1                                   11   00010001 MOVD-5     41    01000001                                                                              MiscGrp-0                                12   00010010 ST-0       42    01000010                                                                              DecD-2                                   13   00010011 AND-0      43    01000011                                                                              RFtoA-0                                  14   00010100 OR-0       44    01000100                                                                              DRJN-1                                   15   00010101 XOR-0      45    01000101                                                                              ItoA-0                                   16   00010110 BTH-0      46    01000110                                                                              RETS-1*.sup.(2)                          17   00010111 BTL-0      47    01000111                                                                              RFtoB-0                                  18   00011000 ADD-0      48    01001000                                                                              INT-5                                    19   00011001 ADC-0      49    01001001                                                                              RFtoRF-0                                 1A   00011010 SUB-0      4A    01001010                                                                              MPY-5                                    1B   00011011 SBB-0      4B    01001011                                                                              ItoB-0                                   1C   00011100 MPY-0      4C    01001100                                                                              TGA-7                                    1D   00011101 CMP-0      4D    01001101                                                                              BtoA-0*.sup.(2)                          1E   00011110 DAC-0      4E    01001110                                                                              INT-1                                    1F   00011111 DSB-0      4F    01001111                                                                              ItoRF-0                                  20   00100000 STA-0      50    01010000                                                                              AtoPPL-0                                 21   00100001 STB-0      51    01010001                                                                              DIRtoA-0*.sup.(2)                        22   00100010 DEC-0      52    01010010                                                                              BtoPPL-0*.sup.(3)                        23   00100011 INC-0      53    01010011                                                                              INDtoA-0*.sup.(3)                        24   00100100 INV-0      54    01010100                                                                              ItoPPL-0                                 25   00100101 CLR-0      55    01010101                                                                              INDXtoA-0                                26   00100110 XCHB-0     56    01010110                                                                              SglAS-0                                  27   00100111 SWAP-0     57    01010111                                                                              SglA-0                                   28   00101000 PUSH-0     58    01011000                                                                              SglBS-0                                  29   00101001 POP-0      59    01011001                                                                              SglB-0                                   2A   00101010 DRJN-0     5A    01011010                                                                              SglRFS-0                                 2B   00101011 DecD-0     5B    01011011                                                                              SglRF-0                                  2C   00101100 RR-0       5C    01011100                                                                              RJMP-0                                   2D   00101101 RRC-0      5D    01011101                                                                              TGC-0                                    2E   00101110 RL-0       5E    01011110                                                                              TGB-0                                    2F   00101111 RLC-0      5F    01011111                                                                              TGA-0                                    80   10000000 ItoPPL-1   E0    11100000                                                                              IAQ-2                                    81   10000001 ItoRF-3*.sup.(3)                                                                          E1    11100001                                                                              INT-0                                    82   10000010 BtoPPL-1*.sup.(2)                                                                         E2    11100010                                                                              MPY-2                                    83   10000011 RFtoA-2    E3    11100011                                                                              BtoPPL-2*.sup.(3)                        84   10000100 RFtoA-1*.sup.(8)                                                                          E4    11100100                                                                              DAC-2                                    85   10000101 ItoA-2     E5    11100101                                                                              TGA-4                                    86   10000110 ItoRF-4*.sup.(2)                                                                          E6    11100110                                                                              DSB-2                                    87   10000111 RFtoB-2    E7    11100111                                                                              INDXtoA-6                                88   10001000 DIRtoA-1*.sup.(2)                                                                         E8    11101000                                                                              RESET-1                                  89   10001001 RFtoRF-2   E9    11101001                                                                              TGA-1                                    8A   10001010 MPY-4      EA    11101010                                                                              MPY-3                                    8B   10001011 ItoB-2*.sup.(2)                                                                           EB    11101011                                                                              JMPL-1                                   8C   10001100 DRJN-3     EC    11101100                                                                              RESET-2                                  8D   10001101 DRJN-2     ED    11101101                                                                              TGA-3                                    8E   10001110 STAL-2     EE    11101110                                                                              TGA-5                                    8F   10001111 ItoRF-2*.sup.(3)                                                                          EF    11101111                                                                              TGA-2                                    90   10010000 PUSH-1     F0    11110000                                                                              LDAP-0                                   91   10010001 DIRtoA-4   F1    11110001                                                                              LDBP-0                                   92   10010010 XCHB-1     F2    11110010                                                                              STP-0                                    93   10010011 INDtoA-2   F3    11110011                                                                              ANDP-0                                   94   10010100 PUSHST-1   F4    11110100                                                                              ORP-0                                    95   10010101 INDXtoA-5  F5    11110101                                                                              XORP-0                                   96   10010110 SWAP-1     F6    11110110                                                                              BTHP-0                                   97   10010111 INDtoA-3   F7    11110111                                                                              BTLP-0                                   98   10011000 SWAP-2     F8    11111000                                                                              MOVD-0                                   99   10011001 TGA-8      F9    11111001                                                                              TEST-0                                   9A   10011010 SglRFS-2   FA    11111010                                                                              LDAL-0                                   9B   10011011 SglRF-2    FB    11111011                                                                              STAL-0                                   9C   10011100 RJMP-3     FC    11111100                                                                              JmpL-0                                   9D   10011101 STAL-1     FD    11111101                                                                              CMPL-0                                   9E   10011110 RJMP-1     FE    11111110                                                                              CALL-0                                   9F   10011111 ItoA-1*.sup.(5)                                                                           FF    11111111                                                                              RESET-0                                  ______________________________________                                          *.sup.(n) microinstruction is shared in n sequences                      

                                      TABLE C                                      __________________________________________________________________________     THE MICROINSTRUCTION SET                                                       Micro-                                                                         Instruction                                                                          Microinstruction Bits                                                                        Operations                                                 __________________________________________________________________________     IAQ-0 (00) First half of instruction fetch; increment PCL via ALU              #PCHtAH             PCH goes to AH bus                                         #PCLtP, #PAL        PCL goes to AL bus via P bus                               default N           All zeros to N bus for input to ALU                        #AluCntl = 0000     Add P and N for increment                                  #ShftCntl = 0001    Carry-In is "1"                                            #OtPCL              ALU output goes to PCL                                     #MEMCNT, #MEM       First half of long read                                    #JmpAddr = (36)     Unconditional jump to IAQ-1                                #JmpCntl = 000                                                                 IAQ-1 (36) Second half of inst. fetch; increment PCH; sample Interrupts        Don't Care to AH, AL                                                                               Address went out on AH', AL' during                                             first half                                                #PCHtP              PCH to P bus for ALU input                                 default N           All zeros to N bus for ALU input                           #AluCntl = 0000     Add P and N                                                #ShftCntl = 0010    Increment on uC of PCL                                     #OtPCH              ALU output goes to PCH                                     #MEM                Secord half of long read                                   # MDtIR             Instruction from memory goes to IR                         #JmpAddr = (E0)     Test for interrupt; if not go to                                                IAQ-2                                                     #JmpCntl = 100                                                                 IAQ-2 (E0) Prefetch B register; Group dispatch to addressing mode              default AH          All zeros to AH bus                                        #ONEtAL             01 on AL bus for B register address                        #PAL                AL to P bus for pass                                       default N           All zeros to N bus for pass                                #AluCntl = 0000     Add P and N for pass P                                     #ShftCntl = 0000    Zero carry in                                              #OtMAL              ALU output (B register address) goes                                            to MAL                                                    #MEM                Short memory read cycle to fetch B                                              register                                                  #MDtT               B register contents loaded into T                                               register from MD bus                                      #JmpAddr = (40)     24-Way Group dispatch based on                                                  contents of IR                                            #JmpCntl = 101                                                                 BtoA-0 (4D) B Register to A Register Addressing Mode; Fetch A Register to      MAL                                                                            default AH, AL      All zeros to AH, AL for A register                                              address                                                   #PAL                Zeros to P bus for pass                                    default             zeros to N bus for pass                                    #AluCntl = 0000     Add P plus N (pass zeros)                                  #ShftCntl = 0000    Zero carry in                                              #OtMAL              Zeros to MAL                                               #MEM                Fetch A Register, result on MD bus                         #JmpAddr = (10)     Function dispatch to DOPFUN, using                         #JmpCntl = 001       function field in IR                                      RFtoA-0 (43) Register file to A Register Addressing Mode; 1st Half of          long                                                                             read; increment PCL                                                          #PCHtAH             Address for immediate fetch                                #PCLtP              PCL to P bus                                               #PAL                PCL to AL via P bus                                        default N           Zeros to N bus for increment                               #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0001    Carry in is 1 to increment PCL                             #OtPCL              Result from ALU back to PCL                                #MEMCNT, #MEM       First half of long read                                    #JmpAddr = (84)     Uncond jump to RFtoA-1 (84)                                #JmpCntl = 000                                                                 RFtoA-1 (84) Second half of Register File Fetch; increment PCH; shared           microstate                                                                   Don't Care to AH, AL                                                                               Address bus continues from previous                                             state                                                     #PCHtP              Set up PCH for increment                                   default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus zeros for increment                             #ShftCntl = 0010    Microcarry uC in from PCL incr                             #OtPCH              Sum to PCH                                                 #MEM                2nd half of long read; data on MD                                               bus                                                       #JmpAddr = (80)     Group Dispatch using field in IR                           #JmpCntl = 101                                                                 RFtoA-2 (83) Fetch register file operand                                       default AH          Zeros to AH for RF address                                 #PAL, #MDtP         Low byte of RF address comes from                                               previous memory fetch                                     default N           Zeros to N bus for pass                                    #AluCntl = 0000     Pass P bus to MAL using Add                                #ShftCntl = 0000    Zero carry-in                                              #OtMAL              Result to MAL via 0 bus                                    #MEM                Short memory read                                          #MDtT               Read source operand into T register                        #JmpAddr = (4D)     Uncond Jump to BtoA-0 for A register                                            fetch                                                     #JmpCntl = 000                                                                 RFtoB-0 (47) Register file to B Register addressing mode; First half of        long                                                                            read; increment PCL                                                           #PCHtAH             Address for immediate fetch                                #PAL, #PCLtP        PCL to AL and P bus                                        default N           Zeros to N for increment                                   #AluCntl = 0000     Add P plus N                                               #ShftCntl =  0001   Carry-in is 1 for increment                                #OtPCL              Result back to PCL                                         #MEMCNT, #MEM       First half of long read                                    #JmpAddr = (84)     Uncond Jump to RFtoA-1                                     #JmpCntl = 000                                                                 RFtoB-2 (87) Fetch RF operand                                                  default AH          Zeros high byte for of RF address                          #MDtP, #PAL         Low byte of RF address comes from                                               previous fetch                                            default N           Zeros to N for pass P                                      #AluCntl = 0000     Add P plus N for pass                                      #ShftCntl = 0000    Zero carry                                                 #OtMAL              Result to MAL                                              #MEM                Short read cycle                                           #MDtT               Read source operand into T register                        #JmpAddr = (8B)     Uncond jump to ItoB-2                                      #JmpCntl = 000                                                                 RFtoRF-0 (49) Register file to register file addressing mode; fetch RF         and                                                                             increment PCL                                                                 #PCHtAH             High byte of address                                       #PCLtP, #PAL        PCL to AL and P bus for RF address                         default N           Zeros to N for increment                                   #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0001    Carry-in is 1 for increment                                #OtPCL              Result back to PCL                                         #MEMCNT; #MEM       First half of long read                                    #JmpAddr = (84)     Uncond jump to RFtoA-1                                     #JmpCntl = 000                                                                 RFtoRF-2 (89) Fetch register file operand                                      default AH          High byte of register file address                         #MDtP, #PAL         Low byte of address comes from                                                  previous fetch                                            default N           Zeros to N for pass P                                      #AluCntl = 0000     Add P plus N for pass                                      #ShftCntl = 0000    Zero Carry                                                 #OtMAL              Result to MAL                                              #MEM                Short read cycle                                           #MDtT               Source operand from RF to T register                       #JmpAddr = (8F)     Uncond jump to ItoRF-2 to fetch                                                 destination operand                                       #JmpCntl = 000                                                                 ItoA-0 (45) Fetch immediate operand; increment PCL                             #PCHtAH             Address for immediate fetch                                #PCLtP, #PAL        PCL to AL and P bus for fetch and                                               increment                                                 default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0001    Carry-in is 1 for increment                                #OtPCL              Result back to PCL                                         #MEMCNT, #MEM       First half of long read                                    #JmpAddr = (9F)     Unconditional jump to ItoA-1                               #JmpCntl = 000                                                                 ItoA-1 (9F) Second half of immediate fetch; increment PCH; shared              microstate                                                                     don't care AH, AL   Address defined in first half                              #PCHtP              Set up PCH for increment                                   default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0010    Micro carry in from PCL increment                          #OtPCH              Result back to PCH                                         #MEM                Second half of long read                                   #MDtT               Source operand to T register                               #JmpAddr = (80)     3-way group dispatch on IR field                           #JmpCntl = 101                                                                 ItoA-2 (85) Fetch Register A as destination operand                            default AH, AL      Zeros to AH and AL for A register                                               address                                                   default P, N        Zeros to P and N busses                                    #AluCntl = 0000     Add F plus N; all zeros                                    #ShftCntl = 0000    Zero carry in                                              #OtMAL              Zeros to MAL                                               #MEM                Short read cycle for A register,                                                result on MD                                              #JmpAddr = (12)     Function dispatch on IR low; DOPFUN                        #JmpCntl = 001                                                                 ItoB-0 (4B) Immediate operand to B register addressing mode                    #PCHtAH             High address for immediate fetch                           #PCLtP, #PAL        PCL to AL and P bus for fetch and                                               increment -default N Zeros to N for increment             #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0001    Carry in is 1 for increment                                #OtPCL              Result back to PCL                                         #MEMCNT, #MEM       First half long read                                       #JmpAddr = (9F)     Jump to ItoA-1 (shared state)                              #JmpCntl = 000                                                                 ItoB-2 (8B) Fetch B register for destination operand                           default AH          Zeros to AH bus for register file                                               address                                                   #ONEtAL             01 to AL bus for B register address                        #PAL                01 to P bus                                                default N           Zeros to N for pass                                        #AluCntl = 0000     Add P plus N for pass                                      #ShftCntl = 0000    Zero carry in                                              #OtMAL              Output to MAL                                              #MEM                Short read cycle for B register,                                                result on MD                                              #JmpAddr = (10)     Function dispatch using IR low; to                                              DOPFUN                                                    #JmpCntl = 001                                                                 ItoRF-0 (4F) Immediate operand to register file mode; increment PCL            #PCHtAH             High byte of address for immed fetch                       #PCLtP, #PAL        PCL to AL and P bus for fetch and                                               increment                                                 default N           Zeros to N                                                 #AluCntl = 0000     Add PCL plus zeros with carry for                                               increment                                                 #ShftCntl = 0001    Carry-in = 1                                               #OtPCL              Result to PCL                                              #MEMCNT, #MEM       1st half of long read                                      #JmpAddr = (9F)     Unconditional jump to ItoA-1                                                    (shared)                                                  #JmpCntl = 000                                                                 ItoRF-2 (8F) Address fetch for register file destination operand;              increment                                                                        PCL                                                                          #PCHtAH             Microcode same as ItoRF-0                                  #PCLtP, #PAL                                                                   default N                                                                      #AluCntl = 0000                                                                #ShftCntl = 0001                                                               #OtPCL                                                                         #MEMCNT, #MEM                                                                  #JmpAddr = (81)     Uncond jump to ItoRF-3                                     #JmpCntl = 000                                                                 ItoRF-3 (81) Second half of register file address fetch                        don't care AH, AL   Address busses continued from                                                   previous cycle                                            #PCHtP              Set up PCH for increment                                   default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0010    Increment on micro carry from PCL                          #OtPCH              Result back to PCH                                         #MEM                Second half of long read                                   #JmpAddr = (86)     Unconditional jump to ItoRF-4                              #JmpCntl = 000                                                                 ItoRF-4 (86) Fetch register file operand                                       default AH          Zeros to AH for register file                                                   address                                                   #MDtP, #PAL         LSH of address comes from fetch in                                              previous state                                            default N           Zeros to N for pass P                                      #AluCntl = 0000     Add P plus N (Pass P)                                      #ShftCntl = 0000    Zero carry in                                              #OtMAL              Result to MAL                                              #MEM                Short read cycle for destination                                                operand                                                   #JmpAddr = (10)     Function dispatch on IR low; to                                                 DOPFUN                                                    #JmpCntl = 001                                                                 AtoPPL-0 (50) Addressing Mode for A register to peripheral page logical;       fetch                                                                            A register to T register as source operand                                   default AH, AH      Zeros for A register address                               don't care P, N     No ALU operation so P, N ALU and                           don't care #AluCntl  carry controls are "don't care"                           don't care #ShftCntl                                                           #MEM                Short read cycle                                           #MDtT               A reg contents to T reg as source                                               operand                                                   #JmpAddr = (52)     Uncond jump to BtoPPL-0                                    #JmptCntl = 000                                                                BtoPPL-0 (52) B Register to Peripheral File; Immed fetch for peripheral          address; Incr. PCL                                                           #PCHtAH             Address for immed fetch                                    #PAL, #PCLtP        PCL to AL bus and P bus                                    default N           Zeros to N                                                 #AluCntl = 0000     Add P plus zeros                                           #ShftCntl = 0001    Carry-in = 1 for incr                                      #OtPCL              Sum back to PCL                                            #MEMCNT, #MEM       1st half of immed fetch                                    #JmpAddr = (82)     Uncond jump to BtoPPL-1                                    #JmpCntl = 000                                                                 BtoPPL-1 (82) Second half of long read for peripheral address fetch;           increment                                                                        PCH                                                                          don't care AH, AL   Address latched from prior state                           #PCHtP              Set up PCH for incr                                        default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus zeros                                           #ShftCntl = 0010    Micro Carry-in for incr PCH                                #OtPCH              Sum to PCH                                                 #MEM                2nd half of long read                                      #JmpAddr = (E3)     Uncond jump to BtPPL-2                                     #JmpCntl = 0000                                                                BtoPPL-2 (E3) Fetch Peripheral Page Operand                                    #ONEtAH             Page address on AH for PF                                  #PAL, #MDtP         AL address comes from fetch in prior                                            state                                                     default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus zeros                                           # ShftCntl = 0000   No carry (pass P)                                          #OtMAL              ALU output (pass P) to MAL                                 #MEMCNT, #MEM       1st half of long read to fetch                                               destination operand from                                                          peripheral page                                           #JmpAddr = (3D)     Uncond jump to BtoPPL-3                                    #JmpCntl = 0000                                                                BtoPPL-3 (3D) 2nd Half Peripheral Page Read                                    don't care AH, AL   2nd half of long read                                      don't care P, N     No ALU operation                                           don't care #AluCntl,                                                           #ShftCntl                                                                      #MEM                Complete long read                                         #JmpAddr = (F0)     Function dispatch; 16-way branch on                                             4-bits of IR; to DOPFUNP                                  #JmpCntl = 001                                                                 ItoPPL-0 (54) Immed operand to Peripheral Page Addressing Mode                 Same microcode as BtoPPL-0 except Uncond jump to ItoPPL-1 (80)                 ItoPPL-1 (80) Immed operand to Peripheral Page; fetch immed to T               register                                                                       Same microcode as BtoPPL-1 plus #MDtT; Uncond jump to BtoPPL-0                 (52)                                                                           SglA-0 (57) Single Operand Addressing Mode, A Register                         default AH, AL      Zeros for A Reg Address on AH, AL                          default P, N        Zeros to P bus and N bus                                   #AluCntl = 0000,    Pass zeros using Add                                        #ShftCntl = 0000                                                              # OtMAL             Result to MAL                                              #MEM, #MDtT         Fetch A to T reg for push                                  #JmpAddr = (28)     Function Dispatch - to SOPFUNN                             #JmpCntl = 001                                                                 SglB-0 (59) Single Operand, B Register                                         Same microcode as SglA-0 except #ONEtAL for B reg address and                  #ALtP to leave B reg address in MAL                                            SglRF-0 (5B) Single Operand, RF                                                Same microcode as BtoPPL-0 except Uncond jump to RFtoA-1 (84)                  SglRF-2 (9B) Fetch RF operand                                                  default AH          zeros for RF page                                          #MDtP, #PAL         MD used as address for fetch and                                                passed to MAL                                             default N           Zeros to N for pass P                                      #AluCntl = 0000,    Pass P using add                                            #ShftCntl = 0000                                                              #OtMAL              Address from MD to MAL                                     #MEM, #MDtT         Read destination operand, to T reg                                              for Push                                                  #JmpAddr = (28),    Function Dispatch - to SOPFUNN                              #JmpCntl = 001                                                                SglAS-0 (56) Single Operand; A Reg; Special Operations                         Same microcode as SglA-0 except no #MDtT; function dispatch to                 (20) SOPFUNS                                                                   SglBS-0 (58) Single Operand; B Reg; Special                                    Same microcode as SglB-0 except no #MDtT; Function Dispatch to                 (20) SOPFUNS                                                                   SglRFS-0 (5A) Single Operand; RF; Special Operations                           Same microcode as SglRF-0; Uncond jump to RFtoA-1 (84)                         SglRFS-2 (9A) Single Operand; RF; Special Operations                           Same microcode as SglRF-2 except no #MDtT; function Dispatch                   to (20) SOPFUNS                                                                INDtoA-0 (53) Indirect through Reg File; Lower reg has high byte of            address,                                                                         upper reg has low byte of address                                            Same microcode as BtoPPL-0; Uncond jump to RFtoA-1 (84) then                   group dispatch                                                                 INDtoA-2 (93) Fetch Low byte of indirect address                               Same microcode as SglRF-2 except #AluCntl = 1111 for subtract                  to decrement RF address to next byte; Uncond jump to INDtoA-3                  (97)                                                                           INDtoA-3 (97) Fetch high byte of indirect address                              default AH          Zeros for RF page                                          #MALtAL             Low byte of RF address                                     default P           Zeros to P bus for pass                                    #TtN                Pass T reg                                                 #AluCntl = 0000;    Pass using add                                              #ShftCntl = 0000                                                              #OtMAL              T reg to MAL                                               #MEM, #MDtT         Read high byte of indirect address                                              to T reg                                                  #JmpAddr = (F9),    Function dispatch, LAFUN                                    #JmpCntl = 001                                                                DIRtoA-0 (51) Direct Two Byte Long Addressing Mode; PC+1 has high byte         of                                                                               address, PC+2 has low byte                                                   Same microcode as BtoPPL-0; Uncond jump to DIRtoA-1 (88)                       DIRtoA-1 (88) 2nd Half high byte address fetch                                 Same microcode as BtoPPL-1, plus #MDtT to store in T reg;                      Uncond jump to INDtoA-0 (53)                                                   DIRtoA-4 (91) Pass low btye of Address to MAL                                  don't care AH, AL   No memory cycle                                            #MDtP               Low byte from memory                                       default N           Zeros to N for pass                                        #AluCntl = 0000,    Pass using add                                              #ShftCntl = 0000                                                              #OtMAL              Result to MAL                                              #JmpAddr = (F9),    Function Dispatch using low IR                              #JmpCntl = 001                                                                INDXtoA-0 (55) Long Indexed Addressing Mode; PC+1 has high byte of Table        Address; PC+2 has low byte                                                    don't care AH, AL   No memory cycle                                            default P           Zeros to P bus for pass                                    #TtN                T reg to N bus                                             #AluCntl = 0000,    Pass N bus to MAL using add                                 #ShftCntl = 0000                                                              #OtMAL              Result to MAL                                              #JmpAddr = (51),    Uncond Jump to DIRtoA(0)                                    #JmpCntl = 000                                                                INDXtoA-5 (95) Add low byte of address to B reg (in MAL)                       don't care AH       No memory cycle                                            #MALtAL, #PAL       MAL (B reg) to P bus via AL bus                            #MDtN               Low byte of table address from MD to                                            N bus                                                     #AluCntl = 0000,    Add for index                                               #ShftCntl = 0000                                                              #OtMAL              Result to MAL                                              #JmpAddr = (E7)     Uncond jump to INDX to A-6                                 #JmpCntl = 000                                                                 INDXtoA-6 (E7) Ripple Carry to High Byte Address                               Don't care AH, AL   No memory cycle                                            default P           Zeros to P bus for increment                               #TtN                High byte of address from T reg to N                                            bus                                                       #AluCntl = 0000,    Pass P; increment if microcarry set                        #ShftCntl = 010      from low byte                                             OtM, #MDtT          Result back to T reg                                       #JmpAddr = (F9),    Function Dispatch to LAFUN                                  #JmpCntl = 001                                                                RJmp-0 (5C) Relative Jump Group; 1st half of Offset Fetch; increment PCL       Same microcode as IAQ-0 except #JmpAddr = (9E), #JmpCntl = 111                 for Macrojump; if Macrojump true go to (9F)                                    RJmp-1 (9E) No Jump; Return to IAQ; Second half of Immed Fetch                 Same microcode as IAQ-1 except #MDtT instead of #MDtIR;                        #JmpAddr = (00), #JmpCntl = 000 for Uncond jump to IAQ-1                       RJmp-3 (9C) Add Offset to PCL; Test if offset negative                         don't care AH, AL   No memory cycle                                            #PCLtP              PCL to P bus                                               #MDtN               Offset to N bus                                            #AluCntl = 0000,    Add PCL plus offset (minus if                               #ShftCntl = 0000    negative)                                                 #OtPCL              Result to PCL                                              #JmpAddr = (3E)     2-way branch on bit-7 of T reg; if                                              offset negative go to RJmp-5                              #JmpCntl = 010                                                                 RJmp-4 (3E) Positive offsets, increment PCH on carry                           Same microcode as RFtoA-1 (84) except no #MEM, and #JmpAddr =                  (00), #JmpCntl = 000 for return to IAQ                                         RJmp-5 (3F) Negative offset, Decrement PCH on borrow                           Same microcode as RJmp-4 except #AluCntl = 1111, subtract for                  decrement on borrow (UC = 0)                                                   MiscGrp-0 (41) Miscellaneous Instruction Group; Fetch top, decrement SP        default AH          High byte of Reg File Address                              #SPtAL              Stack pointer to AL to fetch top                           #ALtP               SP to P bus for decrement                                  default N           Zeros to N bus                                             #AluCntl = 1111,    Decrement P bus                                             #ShftCntl = 0000                                                              #OtMAL              Result back to MAL                                         #MEM                Read top of stack                                          #JmpAddr = (00)     Function Dispatch to MISC                                  #JmpCntl = 001                                                                 TGC-0 (5D) Trap Group C (Addresses FFEF-FFE7); form LSH of trap vector         address                                                                          from IR                                                                      Don't care AH, AL   No memory cycle                                            default P           Zeros to P bus to pass N using Add                         #IRtN               Instruction to N bus                                       #AluCntl = 0000     Add (Pass N)                                               #ShftCntl = 0101    Rotate Left, MSB to LSB                                    #OtMAL              Result (LSH of vector) goes to MAL                         #JmpAddr = (E9)     Uncond jump to TGA-1                                       #JmpCntl = 000                                                                 TGB-0 (5E) Trap Group B (Addresses FFF7-FFF0); form LSH of trap vector         address                                                                          from instruction in IR                                                       Don't care AH, AL   No memory cycle                                            default P           Zeros to P for pass N                                      #IRtN               Instruction to N bus                                       #AluCntl = 0000     Add (Pass N)                                               #ShftCntl =         Rotate left, MSB to LSB                                    #OtMAL              Result to MAL                                              #JmpAddr = (E9)     Uncond Jump to TGA-1                                       #JmpCntl = 000                                                                 TGA-0 (5F) Trap Group A (Addresses FFFF-FFF8); form low byte (LSH) of          trap                                                                             vector address from IR                                                       Microcode same as TGC-0 or TGB-0                                               TGA-1 (E9) Form high byte of Trap Vector Address (of low byte of vector)       don't care AH, AL   No memory cycle                                            default N, P        All zeros for P and N busses                               #AluCntl = 1111     ALU produces all ones by subtract                                               operation                                                 #ShftCntl = 0000    Carry-in = 0                                               #MDtT               OtM asserted; ALU result (all 1's)                                              to T reg                                                  #JmpAddr = (EF)     Uncond jump to TGA-2                                       #JmpCntl = 000                                                                 TGA-2 (EF) First Half Fetch of Low Byte of Vector                              #TtAH               All 1's (FF) from T reg to AH                              #MALtAL, #PAL       Low byte of vector to AL and P                             default N           Zeros to N for decrement                                   #AluCntl = 1111     Subtract                                                   #ShftCntl = 0000                                                               #OtMAL              Result to MAL                                              #MEMCNT, # MEM      First half of long read                                    #JmpAddr = (ED)     Uncond jump to TGA-3                                       #JmpCntl = 000                                                                 TGA-3 (ED) 2nd Half of fetch of low byte of vector                             don't care AH, AL,  No memory cycle and no ALU operation                        P, N, #AluCntl,                                                                #ShftCntl                                                                     #MEM                2nd half long read                                         #JmpAddr = (E5)     Uncond jump to TGA-4                                       #JmpCntl = 000                                                                 TGA-4 (E5) First Half of Fetch of high byte of vector                          #TtAH               FF to AH bus from T reg                                    #MALtAL             Incremented vector to AL                                   #MDtP               Low byte of vector to P bus                                default N           Zeros to N bus for Pass P                                  #AluCntl = 0000     Pass P using Add                                           #ShftCntl = 0000    Zero carry-in                                              #OtMAL              Low byte of vector to MAL                                  #MEMCNT, #MEM       1st half of long read                                      #JmpAddr = (EE)     Uncond jump to TGA-5                                       #JmpCntl = 000                                                                 TGA-5 (EE) 2nd Half of Fetch of High Byte of Vector; increment SP              Don't Care AH       Address latched in first half                              #SPtAL, #PAL        Stack pointer to P bus via AL bus                          default N           Zeros to N bus                                             #AluCntl = 0000     Add operation for increment                                #ShftCntl = 0001    Carry-in = 1                                               #OtSP               Incremented SP back to SP                                  #MEM, #MDtT         2nd Half long read; high byte of                                                vector to T                                               #JmpAddr = (OC)     Uncond jump to TGA-6                                       TGA-6 (OC) Push PCH to Stack                                                   default AH          Zeros to AH for RF address                                 #SPtAL              SP to AL for stack write                                   #PCHtP              PCH to P bus for pass                                      default N           Zeros to N for pass P                                      #AluCntl = 0000     Add operation for pass                                     #ShftCntl = 0000    Carry-in = 0                                               #MEM, #WR           Write PCH to Stack; OtM asserted                           #JmpAddr = (4C)     Uncond jump to TGA-7                                       TGA-7 (4C) Increment Stack Pointer                                             Same Microcode as TGA-5 except no #MEM, #MDtT and #JmpAddr =                   (99) for uncond jump to TGA-8                                                  TGA-8 (99) Write PCL to Stack                                                  Same Microcode as TGA-6 except #PCLtP instead of #PCHtP and                    #JmpAddr = (FC) for uncond jump to JmpL-0                                      ADD-0 (18) Add; Dual Operand Function; Reg File                                default AH          Zeros to AH for RF address                                 #MALtAL             MAL reg to AL bus for RF address                           #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg to N bus                         #AluCntl = 0000     Add P plus N                                               #ShftCntl = 0000    No carry-in                                                #LST                Latch Status                                               #MEM, #WR           Short Memory write cycle, OtM                                                   asserted to write ALU output in                                                destination address                                       #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 0000                                                                ADC-0 (19) Add with carry; dual operand; Reg File                              Microcode same as ADD-0 (18) except #ShftCntl = 0011 for                       status carry bit in                                                            SUB-0 (1A) Subtract; Dual operand function; Register file                      Microcode same as ADD-0 (18) except #AluCntl = 1111, #ShftCntl                 = 0001 for subtract with carry-in = 1                                          SBB-0 (1B) Subtract with borrow                                                Microcode same as SUB-0 except #ShftCntl = 0011 for status                     carry bit in                                                                   DAC-0 (1E) Decimal Add with Carry                                              Microcode given in Text                                                        DAC-1 (30)                                                                     Microcode in Text                                                              DAC-2 (E4)                                                                     Microcode in Text                                                              DSB-0 (1F) Decimal Subtract with borrow                                        Microcode same as DAC-0 except #AluCntl = 1111, #ShftCntl =                    0011 for subtract, carry-in = STC                                              DSB-1 (3C)                                                                     Microcode same as DAC-1 except #AluCntl = 1111                                 DSB-2 (E6)                                                                     Microcode same as DAC-2 except #AluCntl = 1111, #ShiftCntl =                   0001                                                                           CMP-0 (1D) Compare Function; Dual Op; Reg File                                 don't care AH, AL   No memory cycle                                            #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg to N bus                         #AluCntl = 0111     Subtract                                                   #ShftCntl = 0001    Carry-in = 1                                               #LST                Latch Status                                               #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 ST-0 (12) Store Function; Move Source to Destination; Reg File                 default AH          Zeros to AH bus for RF address                             #MALtAL             AL address from MAL                                        default P           Zeros to P bus for pass N                                  #TtN                Source operand from T reg to N bus                         #AluCntl = 0000     Add function for pass                                      #ShftCntl = 0000    No carry-in                                                #LST                Latch Status                                               #MEM, #WR           Generate OtM; write result to dest                                              address                                                   #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 AND-0 (13) AND Function; Dual Operand; Reg File                                default AH          Zeros to AH for RF address                                 #MALtAL             AL address from MAL                                        #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg t N bus                          #AluCntl = 0001     AND function in ALU                                        #ShftCntl = 0000    No carry-in                                                #LST                Latch Status                                               #MEM, #WR           Generate OtM; write result to                                                   distination address                                       #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 OR-0 (14) OR Function                                                          Same microcode as AND-0 except #AluCntl = 0111 for OR                          XOR-0 (15) XOR Function                                                        Same microcode as AND-0 except #AluCntl = 1111 for XOR                         BTH-0 (16) Bit Test, High; Dual Operand; Reg file                              Don't care AH, AL   No memory cycle                                            #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg to N bus                         #AluCntl = 0001     AND function                                               #ShftCntl = 0000    No carry-in                                                #LST                Latch Status                                               #JmpAddr = (44)     Uncond jump to DRJN-1 then RJMP-3                          #JmpCntl = 000                                                                 BTL-0 (17) Bit Test, Low                                                       Same microcode as BTH-0 except #AluCntl = 1011 for inverted-P                  and N                                                                          Multiply operation MPY-0 to MPY-7 performs function of (source) ×         (destination) and stores result in A reg, B reg. MAL is storage for PCL;      IR                                                                              is used for loop count, counts 9 times; PCL is partial product, low byte      of                                                                              answer; B reg is multiplier, low byte of answer; T is multiplicand.           MPY-0 (1C) Write general destination to B reg                                  default AH, #ONEtAL B reg address on AH, AL                                    #MDtP               Destination operand from addressing                                             mode to P bus                                             default N           Zeros to N bus for pass                                    #AluCntl = 0000,    Pass, no carry                                              #ShftCntl = 0000                                                              #MEM, #WR           OtM; write destination operand to B                                             reg                                                       #JmpAddr = (04)     Uncond jump to MPY-1                                       #JmpCntl = 000                                                                 MPY-1 (04) Save PCL in MAL reg                                                 don't care AL, AH    No memory cycle                                           #PCLtP              PCL to P bus for pass                                      default N           Zeros to N bus                                             #AluCntl = 0000,    Pass, no carry                                              #ShftCntl = 0000                                                              #OtMAL              PCL stored in MAL                                          #JmpAddr = (E2)     Uncond jump to MPY-2                                       #JmpCntl = 000                                                                 MPY-2 (E2) Clear count (IR) and partial product (PCL) Registers                don't care AL, AH   No memory cycle                                            default N, P        Zeros to N and P busses for constant                       #AluCntl = 0000,    Pass, no carry                                              #ShftCntl = 0000                                                              #LST                Latch Status                                               #OtPCL              Zeros to PCL (partial product reg)                         OtM, #MDtIR         Zeros to IR (shift count reg)                              #JmpAddr = (EA)     Uncond jump to MPY-3                                       MPY-3 (EA) Rotate Right the Partial Product; fetch multiplier from B reg       default AH, #ONEtAL B reg address on AH, AL                                    #PCLtP              PCL to P bus for rotate                                    default N           Zeros to N bus for pass P                                  #AluCntl = 0000     Pass                                                       #ShiftCntl = 1011   Rotate right, STC to MSB                                   #LST                Latch status; LSB to STC                                   #OtPCL              Partial product back to PCL                                #MEM                Fetch B reg                                                #JmpAddr = (8A)     Uncond jump to MPY-4                                       #JmpCntl = 000                                                                 MPY-4 (8A) Rotate multiplier back to B reg                                     default AH, #ONEtAL B reg address to AH, AL                                    #MDtP               B reg contants from memory to P bus                        default N           Zeros to N                                                 #AluCntl = 0000     Pass                                                       #ShftCntl = 0101    Rotate right, STC to MSB                                   #LST                Latch Status; LSB to STC                                   #MEM, #WR           Multiplier back to B reg                                   #JmpAddr = (4A)     Uncond jump to MPY-5                                       #JmpCntl = 000                                                                 MPY-5 (4A) Increment and rotate shift count; Test STC (Multiplier)             don't care AH, AL   No memory cycle                                            default P           Zeros to P bus                                             #IRtN               Shift Count to N bus                                       #AluCntl = 0000     Pass                                                       #ShftCntl = 0101    Rotate left and increment, gives 9×                                       loop                                                      OtM, #MDtIR         Shift count back to IR                                     #JmpAddr = (34)     Test multiplier bit; if = 1 to                                                  MPY-6; if = 0 to MPY-7 (Jump on                                               status carry bit)                                          #JmpCntl = 110                                                                 MPY-6 (35) If Multiplier bit is 1, T + PCL to PCL                              don't care AH, AL   No memory cycle                                            #PCLtP              Partial Product from PCL to P bus                          #TtN                Multiplicand from T reg to N bus                           #AluCntl = 0000,     Add, multiplicand plus partial                             #ShftCntl = 0000    product of the partial product                            #LST                Latch status, save STC                                     #OtPCL              Sum of multiplicand and partial                                                 product to PCL                                            #JmpAddr = (EA)     Uncond jump to MPY-3 for loop                              #JmpCntl = 000                                                                 MPY-7 (34) If Multiplier bit is zero, clear STC                                default AH, AL      Zeros for A reg address                                    #PCLtP              PCL to P bus to write in A reg                             default N           Zeros to N bus for pass partial                                                 product                                                   #AluCntl = 0000,    Add function, no carry-in for pass P                       #ShftCntl = 0000                                                               #LST                Latch status; zero to STC; set                                                  status on high byte                                       #MEM, #WR           Write to A reg                                             #JmpAddr = (EA)     Test loop count; to MPY-3 or JMPL-1                        #JmpCntl = 011      Jump on uEZ                                                LDAP-0 (FO) Load A (Move to A) Function for Peripheral Page; Move              destination                                                                      operand to A reg                                                             default AH, AL      Zeros for A reg address                                    #MDtP               Destination operand from memory to P                                            bus                                                       default N           Zeros to N bus                                             #AluCntl = 0000     Add P plus zeros (pass P)                                  #ShftCntl = 0000    No carry                                                   #LST                Latch status                                               #MEM, #WR           ALU output to MD Bus (OtM asserted),                                            so result written into A reg                              #JmpAddr = (00)     Jump to IAQ-0                                              #JmpCntl = 000                                                                 LDBP-0 (F1) Load B (Move to B) Function for Peripheral Page; Move              destination                                                                      operand to B reg                                                             Microcode same as LDAP-0 (FO) except #ONEtAL instead of                        default AL to generate B reg address on AL                                     STP-0 (F2) Store Function for Peripheral Page; Move source operand to           destination                                                                   #ONEtAH             Peripheral page address to AH                              #MALtAL             AL address comes from MAL                                  default P           Zeros to P bus                                             #TtN                T reg to N bus                                             #AluCntl = 0000     Add zeros to N (pass)                                      #ShftCntl = 0000    No carry                                                   #LST                Latch status                                               #MEMCNT, #MEM, #WR  1st half of long write; ALU output                                              on MD (OtM)                                               #JmpAddr =          Uncond jump to STAL-2                                      #JmpCntl = 000                                                                 ANDP-0 (F3) And Function for Peripheral Page; Dual Operand                     #ONEtAH             Peripheral page address                                    #MALtAL             AL from MAL                                                #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg to N bus                         #AluCntl = 0001,    Logical, AND                                                #ABL = 1                                                                      #ShftCntl = 0000    No carry                                                   #LST                Latch status                                               #MEMCNT, #MEM, #WR  1st half long write; ALU result on                                              MD (OtM)                                                  #JmpAddr = (8E)     Uncond jump to STAL-2                                      #JmpCntl = 000                                                                 ORP-0 (F4) OR Function for Peripheral Page; Dual Operand                       Microcode same as ANDP-0 (F3) except #AluCntl = 0111, #ABL = 1                 for OR instead of AND                                                          XORP-0 (F5) Exclusive OR Function for Peripheral Page; Dual Operand            Microcode same as ANDP-0 (f3) except #AluCntl = 1111, #ABL = 1                 for XOR                                                                        BTHP-0 (F6) Bit Test High Function, Peripheral; Dual Operand                   Don't Care AH, AL   No memory cycle                                            #MDtP               Destination operand from memory to P                                            bus                                                       #TtN                Source operand from T reg to N bus                         #AluCntl = 0001,    P AND N performed in ALU                                    #ABL = 1                                                                      #ShftCntl = 0000    No carry                                                   #LST                Latch status                                               #JmpAddr = (44)     Uncond jump to DRJN-1                                      #JmpCntl = 0000                                                                BTLP-0 (F7) Bit Test Low Function, Peripheral; Dual Operand                    Microcode same as BTHP-0 (F6) except #AluCntl = 1011, #ABL = 1                 for (Not P) AND N function                                                     PUSH-0 (28) Push Function; Single Operand is in T reg from Addressing          Mode;                                                                            Increment stack Pointer                                                      Don't care AH       No memory cycle                                            #SPtAL, #PAL        SP to ALU via AL and P busses                              default N           Zeros to N                                                 #AluCntl = 0000     Add zeros to SP with carry-in for                                               increment                                                 #ShftCntl = 0001    Carry-in = 1                                               #OtSP               Result back to SP                                          #JmpAdr = 90        Uncond jump to Push-1                                      #JmpCntl = 000                                                                 PUSH-1 (90) Push con't; Write single operand onto stack                        default AH          Zeros to AH for RF address                                 #SPtAL              R address is SP                                            default P           Zeros to P bus                                             #TtN                Operand from T reg to N for pass N                         #AluCntl = 0000     Add zeros to T for pass                                    #ShftCntl = 0000    No carry-in                                                #MEM, #WR           Short memory write; OtM asserted;                                               write T reg contents on stack                             #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 POP-0 (29) Pop Stack; Fetch Top of Stack and Decrement stack Pointer           default AH          Zeros to AH for RF address                                 #SPtAL              RF address is SP                                           #PAL                SP to P for decrement in ALU                               default N           Zeros to N bus                                             #AluCntl = 1111     P minus N minus 1                                          #ShftCntl = 0000    No carry-in                                                #OtSP               Result back to SP                                          #MEM                Read top of stack from RF                                  #MDtT               From memory back to T reg                                  #JmpAddr = (92)     Uncond jump to XCHB-1 for dest write                       #JmpCntl = 000                                                                 DecD-0 (2B) Decrement Double; Least Sig Half Register Decrement, Back to         Memory                                                                       default AH          For RF address                                             #MALtAL             Reg address from MAL                                       #MDtP               LSH from memory to P bus                                   default N           Zeros to N bus for decrement P                             #AluCntl = 1111     Decrement LSH                                              #ShftCntl = 0000                                                               #LST                Latch status; save borrow                                  #MEM, #WR           Write LSH lack to MEM; OtM asserted                        #JmpAddr = (40)     Uncond jump to DecD-1                                      #JmpCntl = 000                                                                 DecD-1 (40) Load Zeros to T (for sharing with SUB microcode)                   Don't Care AL, AH   No memory cycle                                            default N, P        Zeros to N and P busses                                    #AluCntl = 0000     Add zeros                                                  #ShftCntl = 0000    No carry                                                   OtM, #MDtT          ALU output to T reg (zeros)                                #JmpAddr = (42)     Uncond jump to DecD-2                                      #JmpCntl = 000                                                                 DecD-2 (42) Decrement MAL to Point to the Most Sig Half                        Don't Care AH       No memory cycle                                            #MALtAL, #PAL       MAL to P via AL bus                                        default N           Zeros to N bus                                             #AluCntl = 1111     Decrement P bus (MAL Reg)                                  #ShftCntl = 0000                                                               OtM                 Result to MD bus                                           #JmpAddr = (81)     Uncond Jump to ItoRF-4 then to Sub-0                       #JmpCntl = 000                                                                 DRJN-0 (2A) Decrement Reg and Jump on Not Zero; First State decrements         and                                                                              writes back, set u zero                                                      default AH          RF address is zeros on AH                                  #MALtAL             RF address is destination in MAL                           #MDtP               Destination operand to P bus from                                               memory                                                    default N           Zeros on N bus for decrement                               #AluCntl = 1111     Subtract for decrement; set u zero                         #ShftCntl = 0000                                                               #MEM; #WR           Write ALU output via OtM to                                                     destination                                               #JmpAddr = (44)     Uncond jump to DRJN-1                                      #JmpCntl = 000                                                                 DRJN-1 (44) Con't; 1st half of Offset Fetch                                    #PCHtAH             PCH to address high and                                    #PCLtP, #PAL        PCL to address low to fetch immed                                               offset                                                    default N           Zeros to N bus for increment P                             #AluCntl = 0000     Add P bus (PCL) to zeros, carry-in =                                            1                                                         #ShftCntl = 0001    Carry-in = 1 for increment                                 #OtPCL              Result back to PCL                                         #MEMCNT, #MEM       1st half of long read                                      #JmpAddr = (8C)     "Micro equal zero" dispatch; if                                                 UEZ = 1 go to DRJN-1 (8D), else to                                             DRJN-3 (8C)                                               #JmpCntl =  011                                                                DRJN-2 (8D) Con't; No jump, return to IAQ; 2nd half of Immed Fetch             Don't care AH, AL   No memory cycle                                            #PCHtP              PCH to P bus                                               default N           Zeros to N for increment                                   #AluCntl = 0000     Add P bus (PCH) plus zeros                                 #ShftCntl = 0010    Micro carry-in; increment PCH if                                                carry from PCL                                            #OtPCH              Result back to PCH                                         #MEM; #MDtT         2nd half long read; offset back to T                                            reg                                                       #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 DRJN-3 (8C) Con't; Jump Condition Valid; 2nd Half Immed Fetch                  Microcode same as DRJN-2 (8D) except #JmpAddr = (9C) to go to                  RJMP-3 to complete relative jump                                               RR-0 (2C) Rotate Right Circular; Single Operand Function                       default AH          Zeros for RF address on AH                                 #MALtAL             RF address in MAL from addressing                                               mode                                                      #MDtP               Destination operand from memory to P                                            bus                                                       default N           Zeros to N for pass P                                      #AluCntl = 0000     Add zeros to P                                             #ShftCntl = 1001    Rotate right, carry-in = 0                                 #LST                Latch status                                               #MEM, #WR           Result to MD; OtM asserted; write in                                            destination address                                       #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 RRC-0 (2D) Rotate Right Thru Carry                                             Microcode same as RR-0 (2C) except #ShftCntl = 1011 for rotate                 right thru carry                                                               RL-0 (2E) Rotate Left Circular; shared as 4th rotate in Swap Function          Microcode same as RR-0 (2C) except #ShftCntl = 0101 for rotate                 left                                                                           RLC-0 (2F) Rotate Left Thru Carry                                              Microcode same as RR-0 (2C) except #ShftCntl = 0111 for rotate                 left thru carry                                                                STA-0 (20) Store A (Move from A) Function; Fetch A Reg to Move to B Reg        or RF                                                                          a default AH, AL    Zeros for Reg A address                                    Don't Care P, N,    No ALU operation                                            #AluCntl                                                                      #MEM, #MDtT         Read A reg to T reg                                        #JmpAddr = (21)     Uncond jump to STB-0 to write A reg                                             to destination address                                    STB-0 (21) Store B (Move from B) Function; Move T Reg to Destination           Address                                                                          in MAL; used for MOV A,B; MOV A, RF; MOV B, RF; TST A; TST B                 default AH          Zeros on AH for RF address                                 #MALtAL             Destination addess to AL                                   default P           Zeros to P bus                                             #TtN                Source operand from T reg to N bus                         #AluCntl = 0000     Pass destination operand                                   #ShftCntl = 0000    Carry-in = 0                                               #LST                Latch status                                               #MEM, #WR           Result via OtM to destination                                                   address in RF                                             #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 DEC-0 (22) Decrement; Single Operand Function                                  Microcode same as Decrement Double DecD-0 (2B) except #JmpAddr                 = (00); #JmpCntl = 000 for return to IAQ                                       INC-0 (23) Increment; Single Operand Function                                  Microcode same as DEC-0 (22) except #AluCntl = 0000; #ShftCntl                 = 0001 for add-1 or increment                                                  INV-0 (24) Invert; Single Operand Function                                     default AH          Zeros to AH for RF address                                 #MALtAL             RF address is in MAL from addressing                                            mode                                                      #MDtP               Destination operand from memory to P                                           bus                                                        don't care N        One operand so N bus is don't care                         #AluCntl = 1010,    Invert P                                                    #ABL = 1                                                                      #ShftCntl = 0000    Carry-in 0                                                 #LST                Latch status                                               #MEM, #WR           Write result via OtM to destination                                             address                                                   #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 CLR-0 (25) Clear; Single Operand Function                                      Microcode same as INV-0 (24) except #AluCntl = 1001 for zeros                  XCHB-0 (26) Exchange B Reg with Destination Operand; 1st state-write            destination operand in B reg.                                                 default AH          Zeros to AH for RF address                                 #ONEtAL             B reg address to AL                                        #MDtP               Destination operand from memory to P                                            bus                                                       default N           Zeros to N bus for pass P                                  #AluCntl = 0000     Add P plus zeros                                           #ShftCntl = 0000    Carry-in = 0                                               #LST                Latch status                                               #MEM, #WR           Write via OtM to B reg                                     #JmpAddr = (92)     Uncond jump to XCHB-1                                      #JmpCntl = 000                                                                 XCHB-1 (92) Write B Reg to Destination Location                                default AH          Zeros to AH for RF address                                 #MALtAL             MAL to AL for destination address                          default P           Zeros to P bus for pass N                                  #TtN                B reg operand from T reg to N bus                          #AluCntl = 0000     Add zeros to N using Add                                   #ShftCntl = 0000    No carry-in                                                #MEM, #WR           Memory writes; generate OtM; T reg                                              contents thru ALU to Destination                          #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 SWAP-0 (27) Single Operand Swap function; First rotate back to MD bus          don't care AH, AL   No memory cycle                                            #MDtP               Operand from ALU to P bus                                  default N           Zeros to N bus for pass P                                  #AluCntl = 0000     Add zeros to P for Pass                                    #ShftCntl = 0101    Shift is "rotate left circular"                            #OtM                Result back to MD bus                                      #JmpAddr = (96)     Uncond jump to SWAP-1                                      #JmpCntl = 000                                                                 SWAP-1 (96) Second rotate back to MD bus                                       Same microcode as SWAP-0 (27); uncond jump to SWAP-2                           SWAP-2 (98) Third rotate back to MD bus                                        Same as SWAP-0 (27); uncond jump to RL-0 (2E) for 4th rotate                   to complete byte swap                                                          LDAL-0 (FA) Load A Reg From Long Addressing Mode; 1st Half of Long             Operand                                                                        Read                                                                           #TtAH               T Reg has high byte of long address                        #MALtAL             MAL has low byte of long address                           default P, N        Zeros to P and N busses for pass                                                zero                                                      #AluCntl = 0000     Pass zeros by Add operation                                #ShftCntl = 0000    No carry-in                                                #OtMAL              Zeros to MAL (to share STB-0)                              #MEMCNT, #MEM       1st half long read                                         #JmpAddr = (20)     Uncond jump to STA-0 to read 2nd,                                               write A                                                   #JmpCntl = 000                                                                 STAL-0 (FB) Store A Reg to Long Addressing Mode; Read A Reg                    default AH, AL      A Reg address is all zeros                                 Don't care P, N,    No ALU cycle                                                #AluCntl, #ShftCntl                                                           #MEM                Read A Reg; contents on MD bus                             #JmpAddr = (9D)     Uncond jump to STAL-1                                      #JmpCntl = 000                                                                 STAL-1 (9D) Store A Long Write Operation                                       #TtAH               T has address high                                         #MALtAL             MAL has address low                                        #MDtP               A coming from memory to P bus                              default N           Zeros to N bus for pass                                    #AluCntl = 0000     Add operation for pass                                     #ShftCntl = 0000    No carry-in                                                #LST                Latch status                                               #MEMCNT; #MEM, #WR  1st half long write; ALU to MD by                                               OtM                                                       #JmpAddr = (8E)     Uncond jump to STAL-2                                      #JmpCntl = 000                                                                 STAL-2 (8E) Store A Long Write (con't)                                         default AH          Zeros to AH for RF                                         #ONEtAL             0001 to AL for B Reg address                               #MDtP               Result from prior state from MD to P                                            bus                                                       default N           Zeros to N for Pass                                        #AluCntl = 0000     Pass MD back around to MD                                  #ShftCntl = 0000    No carry-in                                                #MEM, #WR           Generates OtM; 2nd half of long                                                 write                                                     #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl - 000                                                                 CMPL-0 (FD) Compare Long; 1st Half of Long Operand Fetch                       #TtAH               T Reg has high byte of address                             #MALtAL             MAL Reg has low byte of address                            Don't Care P, N                                                                Don't Care #AluCntl,                                                                               No ALU cycle                                                #ShftCntl                                                                     #MEMCNT, #MEM       1st half of long read                                      #JmpAddr = (83)     Uncond jump to RFtoA-2                                     #JmpCntl = 000                                                                 JmpL-0 (FC) Long Jump Function; Enters with High byte in T reg, Low Byte       in                                                                               MAL                                                                          Don't Care AH, AL   No memory cycle                                            default P           Zeros to P bus                                             #TtN                T reg (High byte of long address) to                                            N bus                                                     #AluCntl = 0000     Pass N using Add                                           #ShftCntl = 000     No carry-in                                                #OtPCH              ALU output to PCH                                          #JmpAddr = (EB)     Uncond jump to JmpL-1                                      #JmpCntl = 000                                                                 JmpL-1 (EB) Jump Long; Move Low byte of address to PCL                         don't care AH       No memory cycle                                            #MALtAL, #PAL       Low byte to P bus via AL bus                               default N           Zeros to N for pass P bus                                  #AluCntl = 0000     Pass P using Add                                           #ShftCntl = 0000    No carry-in                                                #OtPCL              Low byte from ALU to PCL                                   #JmpAddr = (00)     Uncond jump to IAQ                                         #JmpCntl = 000                                                                 Call-0 (FE) Long Call Function; Enters with high byte of address in T          reg, low                                                                         byte in MAL                                                                  Don't care AH       No memory cycle                                            #SPtAL, #PAL        SP to P bus via AL bus                                     default N           Zeros to N bus                                             #AluCntl = 0000     Zeros with carry for increment                             #ShftCntl = 0001    Carry-in = 1                                               #OtSP               Incremented SP back to SP                                  #JmpAddr = (OC)     Uncond jump to trap sequence TGA-6                         #JmpCntl = 000                                                                 MOVD-0 (F8) Move Double; Enters with high byte data in T Reg, low byte in      MAL;                                                                             Must fetch reg address (of low byte data), decrement to write high           byte;                                                                            first state is move low byte to IR, free MAL                                 Don't care AH       No memory cycle                                            #MALtAL, #PAL       MAL to P via AL bus to pass to IR                          #default N          Zeros to N bus for pass                                    #AluCntl = 0000     Add operation for pass                                     #ShftCntl = 0000    No carry-in                                                OtM, #MDtIR         ALU result to IR via MD bus                                #JmpAddr = (31)     Uncond jump to MOVD-1                                      #JmpCntl = 000                                                                 MOVD-1 (31) 1st Half of Reg address fetch; increment PCL                       #PCHtAH             Address for Immed fetch                                    #PCLtP, #PAL        PCL to AL and P bus                                        default N           Zeros to N bus                                             #AluCntl = 0000     Add for increment PCL                                      # ShftCntl = 0001   Carry-in = 1                                               #OtPCL              Result back to PCL                                         #MEMCNT, #MEM       1st half long read                                         #JmpAddr = (33)     Uncond jump to MOVD-2                                      #JmpCntl = 000                                                                 MOVD-2 (33) 2nd Half of RF address fetch; increment PCH                        don't care AH, AL   2nd half of long read                                      #PCHtP              PCH to P bus                                               default N           Zeros to N bus                                             #AluCntl = 0000     Add zeros to PCH with microcarry                                                from PCL                                                  #ShftCntl = 0010                                                               #OtPCH              Result back to PCH                                         #MEM                2nd half of long read; leaves                                                   address of RF on MD                                       #JmpAddr = (37)     Uncond jump to MOVD-3 (37)                                 #JmpCntl = 000                                                                 MOVD-3 (37) Move RF Address to MAL                                             don't care AH, AL   No memory cycle                                            #MDtP               RF address from memory to P bus                            default N           Zeros to N for pass                                        #AluCntl = 0000     Pass using Add                                             #ShftCntl = 0000    No carry-in                                                #OtMAL              Result to MAL; address of low byte                                              date                                                      #JmpAddr = (10)     Uncond jump to MOVD-4                                      #JmpCntl = 000                                                                  MOVD-4 (10) Write low byte reg to memory                                      default AH          Zeros to AH for RF                                         #MALtAL             Reg Address to MAL                                         default P           Zeros to P bus                                             #IRtN               Low byte reg address from IR to N                                               bus                                                       #AluCntl = 0000     Pass N                                                     #ShftCntl = 0000    No carry-in                                                #MEM, #WR           OtM; write low byte to memory                              #JmpAddr = (11)     Uncond jump to MOVD-5                                      #JmpCntl = 000                                                                 MOVD-5 (11) Decrement MAL to Point to High byte                                don't care AH       No memory cycle                                            #MALtAL, #PAL       MAL to P bus via AL bus                                    default N           Zeros to N bus for decrement                               #AluCntl = 1111,    Decrement P bus (subtract in ALU)                           #ABL = 0                                                                      #ShftCntl = 0000    No carry-in                                                #OtMAL              Result to MAL                                              #JmpAddr = (92)     Uncond jump to XCHB-1                                      #JmpCntl = 000                                                                 Test-0 (F9) Test Sequence; Enters test function from long addressing mode      with                                                                             high byte of address in T reg, low byte in MAL                               #TtAH               T reg has high byte of ROM address                         #MALtAL             MAL has low byte of ROM address                            default P, N        Zeros to P and N busses to create 02                                            constant                                                  #AluCntl = 0000     ALU function is 0 + 0 + 1, rotate                                               left, equals 02                                           #ShftCntl = 0100    Carry-in = 1; shift left                                   #MDtIR              ALU result to IR for AtoPPL mode                           #MEMCNT, #MEM       1st half of long read (generates                                                OtM)                                                      #JmpAddr = (50)     Uncond jump to AtoPPL-0, then STP-0                                             function                                                  #JmpCntl = 000                                                                 PopST-0 (08) Pop Stack; Fetch Top of Stack and Decrement Stack Pointer         default AH          Zeros to AH for RF address                                 #SPtAL, #PAL        Stack Pointer to AL and P                                  default N           Zeros to N                                                 #AluCntl = 1111     Subtract for decrement SP                                  #ShftCntl = 0000    Zero carry-in                                              #OtSP               Result back to SP                                          #MEM, #MDtT         Read top from RF to T Reg                                  #JmpAddr = (OF)     Uncond jump to LDST-0 (OF)                                 #JmpCntl = 000                                                                 RETS-0 (OA) Return from Subroutine Function; Move Top of Stack to PCL          Don't Care AH, AL   No memory cycle                                            #MDtP               Top of stack on MD goes to P bus                           default N           Zeros to N bus for pass                                    #AluCntl = 0000     Add operation for pass P                                   #ShftCntl = 0000    Carry-in = 0                                               #OtPCL              Result to PCL                                              #JmpAddr = (46)     Uncond jump to RETS-1                                      #JmpCntl = 000                                                                 RETS-1 (46) Fetch Top of Stack; Decrement SP                                   default AH          Zeros to AH for RF address                                 #MALtAL, #PAL       MAL to AL and P                                            default N           Zeros  N bus for decrement                                 #AluCntl = 1111     Subtract                                                   #ShftCntl = 0000    Zero carry-in                                              #OtSP               Result back to SP                                          #MEM                Read top of stack                                          #JmpAddr = (3A)     Function dispatch to (3A) or (3B) on                                            IR low                                                    #JmpCntl = 001                                                                 RETS-2 (3A) Write Top to PCH Reg                                               Same microcode as RETS-0 except #OtPCH instead of #OtPCL;                      #JmpAddr = (00) for uncond jump to IAQ-0                                       RETI-0 (OB) Return From Interrupt; Fetch Top                                           Same microcode as RETS-0; #JmpAddr = (46), RETS-1                      RETI-2 (3B) Fetch Top; Decrement SP                                            Same microcode as RETS-2 except #JmpAddr =  (08) for uncond                    jump to PopST-0                                                                STSP-0 (09) Store Stack Pointer into B Reg; Pass SP to MD bus                  don't care AH       No memory cycle                                            #SPtAL, #PAL        SP to P bus via AL bus                                     default N           Zeros to N bus                                             #AluCntl = 0000     Add function for Pass P                                    #ShftCntl = 0000    Carry-in = 0                                               OtM                 Result to MD bus                                           #JmpAddr = (8E)     Uncond jump to STAL-2 to write SP to                                            B reg                                                     #JmpCntl = 000                                                                 LDSP-0 (OD) Load Stack Pointer From B Reg; Write B Reg from T to SP            don't care AH, AL   No memory cycle                                            default P           Zeros to P bus                                             #TtN                T Reg (B Reg) to N Bus                                     #AluCntl = 0000     Add function for Pass T                                    #ShftCntl = 0000    Carry-in = 0                                               #OtSP               Result to Stack Pointer                                    #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 #PushST-0 (OE) Push Stack Function; increment SP                               don't care AH       No memory cycle                                            #SPtAL, #PAL        SP to AL and P bus                                         default N           Zeros to N                                                 #AluCntl = 0000     Add function for pass P                                    #ShftCntl = 0001    Carry-in = 1 for increment                                 #OtSP               Result to SP                                               #JmpAddr = (94)     Uncond jump to PushST-1                                    #JmpCntl = 000                                                                 #PushST-1 (94) Write Status on Stack                                           default AH          Zeros to AH for RF address                                 #SPtAL              SP to AL for stack address                                 default P           Zeros to P bus for pass N                                  #STtN               Status Reg to N bus                                        #AluCntl = 0000     Pass N using Add                                           #ShftCntl = 0000    Carry-in = 0                                               #MEM, #WR           OtM asserted; write to stack                               #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 #LDST-0 (OF) Load Status From B Reg (Not used as macroinstruction); Write        Reg to Status                                                                don't care AH, AL   No memory cycle                                            default P           Zeros to P bus                                             #TtN                B Reg from T Reg to N bus                                  #AluCntl = 0000     Pass N                                                     #ShftCntl = 0000    Carry-in = 0                                               #OtST               Result to ST                                               #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 EINT-0 (05) Enable Interrupt; Write all ones into Status Reg                   don't care AH, AL   No memory cycle                                            default P, N        Zeros to P and N                                           #AluCntl = 1111     Subtract produces all ones                                 #ShftCntl = 0000    Carry-in = 0                                               #OtST               Ones to ST                                                 #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 DINT-0 (06) Disable Interrupt; Write all zeros into Status Reg                 don't care AH, AL   No memory cycle                                            default P, N        Zeros to P and N                                           #AluCntl = 0000     Pass zeros                                                 #ShftCntl = 0000    Carry-in = 0                                               #OtST               Zeros to ST                                                #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 IDLE-0 (01) Idle Function; Decrement PCL                                       don't care AH, AL   No memory cycle                                            #PCLtP              PCL to P bus                                               default N           Zeros to N for decrement                                   #AluCntl = 1111,    Subtract for decrement; carry-in = 0                        #ShftCntl = 0000                                                              #OtPCL              Result back to PCL                                         #JmpAddr = (38)     Uncond jump to IDLE-1                                      #JmpCntl =  000                                                                IDLE-1 (38) Idle Function; Decrement PCH if borrow                             don't care, AH, AL  No memory cycle                                            #PCHtP              PCH to P bus                                               default N           Zeros to N for decrement P                                 #AluCntl = 1111     Subtract                                                   #ShftCntl = 0010    uC in                                                      #OtPCH              Result to PCH                                              #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 SetC-0 (07) Set Carry; Clear Sign Bit; Sets Zero Bit                           don't care AH, AL   No memory cycle                                            default P, N        Zeros to P and N                                           #AluCntl = 1111     0 - 0 = 0                                                  #ShftCntl = 0001    STC = 1                                                    #LST                Load Status                                                #JmpAddr = (00)     Uncond jump to IAQ-0                                       #JmpCntl = 000                                                                 INT-0 (E1) Interrupt Routine; Int Ack; Subtract for Idle Test                  default AH, AL      Zeros to AH, AL busses to put out                                               known value during Int Acknowledge                        #MDtP               Instruction to P bus for Idle Test                         default N           Zeros to N bus for decrement                               #AluCntl = 1111     Subtract one to check for zero                             #ShftCntl = 0000    Carry-in =  0                                              #MEMCNT             1st half of Int Ack; asserts Int Ack                       #JmpAddr = (4E)     Uncond jump to INT-1                                       #JmpCntl = 000                                                                 INT-1 (4E) Interrupt Routine; Increment SP; Test for Zero (Idle)               don't care AH       Address latched during INT-0                               #SPtAL, #PAL        SP to AL bus and P bus                                     default N           Zeros to N for increment                                   #AluCntl = 0000     Add for increment                                          #ShftCntl = 0001    Carry-in = 1                                               #OtSP               Result bck to SP                                           #MDtIR              Vector from device to IR; Int Ack                                               asserted                                                  #JmpAddr = (02)     Jump on micro equal zero; if Idle go                                            to INT-4, else go to INT-2                                #JmpCntl = 011                                                                 INT-2 (02) Decrement PCL for all instructions except idle                      don't care AH       No memory cycle                                            #PAL, #PCLtP        PCL to P bus via AL                                        default N           Zeros to N for decrement                                   #AluCntl = 1111     Subtract to decrement PCL                                  #ShftCntl = 0000    Carry-in = 0                                               #OtPCL              Result back to PCL                                         #JmpAddr = (39)     Uncond jump to INT-3                                       #JmpCntl = 000                                                                 INT-3 (39) Decrement PCH if Borrow from PCL                                    don't care AH, AL   No memory cycle                                            #PCHtP              PCH to P bus                                               default N           Zeros to N bus                                             #AluCntl = 1111     Decrement PCH if borrow                                    #ShftCntl = 0010    uC in                                                      #OtPCH              Result to PCH                                              #JmpAddr = (03)     Uncond jump to INT-4                                       #JmpCntl = 000                                                                 (NOTE: Interrupts are one address apart because they share the trap code       which rotates the address left.)                                               INT-4 (03) Write Status to Stack                                               default AH          Zeros to AH for RF address                                 #SPtAL              SP to AL for stack write                                   default P           Zeros to P bus for pass N                                  #STtN               Status Reg to N bus                                        #AluCntl = 0000     Pass N bus using Add                                       #ShftCntl = 0000    Carry-in = 0                                               #MEM, #WR           Write Status Reg to Stack                                  #JmpAddr = (48)     Uncond jump to INT-5                                       #JmpCntl = 000                                                                 INT-5 (48) Clear Int Enable in Status                                          don't care AH, AL   No memory cycle                                            default P, N        Zeros to P and N busses                                    #AluCntl = 0000     ALU all zeros                                              #ShftCntl = 0000    Carry-in = 0                                               #OtST               Zeros to Status Reg                                        #JmpAddr = (5F)     Uncond jump to TGA-0                                       #JmpCntl = 000                                                                 RESET-0 (FF) Reset sequence; Don't Care State                                  don't care AH, AL   No memory cycle                                            don't care P, N     No ALU cycle                                               don't care #AluCntl,                                                            #ShftCntl                                                                     #MEM                Read cycle to protect memory from                                               Long Write                                                #JmpAddr = (E8)     Uncond jump to RESET-1                                     #JmpCntl = 000                                                                 RESET-1 (E8) Reset; ALU produces FF as vector address                          don't care AH, AL   No memory cycle                                            default P, N        Zeros to P and N busses                                    #AluCntl = 1111     Subtract to produce all ones                               #ShftCntl = 0000    Carry-in = 0                                               #OtSP               Ones to SP                                                 #MDtT, #MDtIR       OtM asserted; ones to IR for high                                               byte address; ones to T                                   #JmpAddr = (EC)     Uncond jump to RESET-2                                     #JmpCntl = 000                                                                 RESET-2 (EC) Reset; Write zeros to Interrupt Control Reg                       #ONEtAH             PF address                                                 default AL          Zeros to AL for 0100 Int Cont Reg                                               Address                                                   default P, N        Zeros to P and N for pass zeros                            #AluCntl = 0000     ADD 0 + 0                                                  #ShftCntl = 0000    Carry-in = 0                                               #OtSt               Zeros to Staus Reg                                         #MEMCNT, #MEM, #WR  1st half long write to Int Cont Reg                        #JmpAddr = (32)     Uncond jump to RESET-3 for 2nd half                                             of long write                                             #JmpCntl = 000                                                                 RESET-3 (32) RESET; 2nd Half of Long Write                                     don't care AH, AL   Address is latched in RESET-2                              default P, N        Zeros to P and N busses                                    #AluCntl = 0000     Pass zeros again for long write                            #ShftCntl = 0000    Carry-in = 0                                               #MEM, #WR           2nd half long write; OtM asserted                          #JmpAddr = (5F)     Uncond jump to TGA-0 to form vector                        #JmpCntl = 000                                                                 __________________________________________________________________________

                  TABLE D                                                          ______________________________________                                         #AluCntl          ALU Output                                                   3   2     1     0   #ABL  to Shifter S                                                                               Operations                               ______________________________________                                         0   0     0     0   0     P + N + Cin Add                                      0   0     0     0   1     P XNOR N    Exclusive NOR                            0   0     0     1   1     P AND N     AND                                      0   0     1     0   1     (NOT P) OR N                                                                               OR                                       0   0     1     1   1     N           Pass N                                   0   1     0     0   1     P OR (NOT N)                                                                               OR                                       0   1     0     1   1     P           Pass P                                   0   1     1     0   1     FF(hex)     all 1's                                  0   1     1     1   1     P OR N      OR                                       1   0     0     0   1     P NOR N     NOR                                      1   0     0     1   1     00          All 0's                                  1   0     1     0   1     NOT P       Invert P                                 1   0     1     1   1     (NOT P) AND N                                                                              AND                                      1   1     0     0   1     NOT N       Invert N                                 1   1     0     1   1     P AND (NOT N)                                                                              AND                                      1   1     1     0   1     P NAND N    NAND                                     1   1     1     1   0     P - N - 1 + Cin                                                                            Subtract                                 1   1     1     1   1     P XOR N     Exclusive OR                             ______________________________________                                    

                                      TABLE E                                      __________________________________________________________________________     GROUP DISPATCH                                                                 Selection of Addressing Model                                                  __________________________________________________________________________     FORMAT "0"                FORMAT "1"                                           IR     CROM ADDRESS                                                                             MICRO-   IR     CROM ADDRESS                                                                             MICRO-                              CONTENTS                                                                              HEX BINARY                                                                               INSTRUCTION                                                                             CONTENTS                                                                              HEX BINARY                                                                               INSTRUCTION                         __________________________________________________________________________     0000XXXX                                                                              41  01000001                                                                             MISC-0   10000XXX                                                                              50  01010000                                                                             AtoPPL-0                            0001XXXX                                                                              43  01000011                                                                             RFtoA-0  10001XXX                                                                              51  01010001                                                                             DIRtoA-0                            0010XXXX                                                                              45  01000101                                                                             ItoA-0   10010XXX                                                                              52  01010010                                                                             BtoPPl-0                            0011XXXX                                                                              47  01000111                                                                             RFtoB-0  10011XXX                                                                              53  01010011                                                                             INDtoA-0                            0100XXXX                                                                              49  01001001                                                                             RFtoRF-0 10100XXX                                                                              54  01010100                                                                             ItoPPL-0                            0101XXXX                                                                              4B  01001011                                                                             ItoB-0   10101XXX                                                                              55  01010101                                                                             INDXtoA-0                           0110XXXX                                                                              4D  01001101                                                                             BtoA-0   10110XXX                                                                              56  01010110                                                                             SglAS-0                             0111XXXX                                                                              4F  01001111                                                                             ItoRF-0  10111XXX                                                                              57  01010111                                                                             SglA-0                                                        11000XXX                                                                              58  01011000                                                                             SglBS-0                                                       11001XXX                                                                              59  01011001                                                                             SglB-0                                                        11010XXX                                                                              5A  01011010                                                                             SglRFS-0                                                      11011XXX                                                                              5B  01011011                                                                             SglRF-0                                                       11100XXX                                                                              5C  01011100                                                                             RJmp-0                                                        11101XXX                                                                              5D  01011101                                                                             TGC-0                                                         11110XXX                                                                              5E  01011110                                                                             TGB-0                                                         11111XXX                                                                              5F  01011111                                                                             TGA-0                               __________________________________________________________________________      ##STR1##                                                                       ##STR2##                                                                 

    TABLE F                                                                        ______________________________________                                         FUNCTION DISPATCH                                                              Selection of Function to be Executed For Dual Operand Function                 ______________________________________                                         OPCODE:    CROM Address                                                        IR Contents                                                                               Hex      Binary   Microinstruction                                  ______________________________________                                         0XXX0010   12       00010010 ST-0                                              0XXX0011   13       00010011 AND-0                                             0XXX0100   14       00010100 OR-0                                              0XXX0101   15       00010101 XOR-0                                             0XXX0110   16       00010110 BTH-0                                             0XXX0111   17       00010111 BTL-0                                             0XXX1000   18       00011000 ADD-0                                             0XXX1001   19       00011001 ACD-0                                             0XXX1010   1A       00011010 SUB-0                                             0XXX1011   1B       00011011 SBB-0                                             0XXX1100   1C       00011100 MPY-0                                             0XXX1101   1D       00011101 CMP-0                                             0XXX1110   1E       00011110 DAC-0                                             0XXX1111   1F       00011111 DSB-0                                             ______________________________________                                         CROM Address = Base address bits J7, J6, J5, J4 (here hex 10);                 plus function field of OPCODE (IR3, IR2, IR1, IR0)                              ##STR3##                                                                 

    TABLE G                                                                        ______________________________________                                         SUMMARY OF DISPATCH MODES                                                               Microcode                                                                      Bits                                                                  Dispatch #JmpCntl                                                              Mode     2     1     0   OPERATION                                             ______________________________________                                         Unconditional                                                                           0     0     0   Unconditional jump to                                                          #JmpAddr(7-0) location.                               Function 0     0     1   Function dispatch; 16-way branch on                                            low-order 4 bits of IR                                Test sign bit                                                                           0     1     0   2-way branch on T(7), MSB of T Reg                    Test if zero                                                                            0     1     1   Micro equal zero, uEZ, bit from                                                ALU tested.                                           Test for 1     0     0   Interrupt Active bit is tested                        interrupt                                                                      Group    1     0     1   Group Dispatch - 24-way branch on                                              high order 5 bits of IR.                              Test if carry                                                                           1     1     0   Test STC bit                                          Test Status                                                                             1     1     1   Macro jump; test status bits                                                   dependent on low-order 3 bits of IR.                  Reset    X     X     X   Forces μA to FF unconditionally,                                            regardless of current #JmpAddr or                                              #JmpCntl bit                                          ______________________________________                                    

                                      TABLE H                                      __________________________________________________________________________     MEMORY CONTROL                                                                 #MEMCNT                                                                               #MEMCNT                                                                 (current)                                                                             (previous)                                                                            #MEM #WR Memory Reference                                                                           OtM                                         __________________________________________________________________________     0      0      0    0                                                           No Mem Reference -                 0                                           0      0      0    1   Gate O Bus to MD Bus                                                                       1                                           0      0      1    0   Short Memory Read                                                                          0                                           0      0      1    1   Short Memory Write                                                                         1                                           0      1      0    0   2nd State Int. Vector                                                                      0                                           0      1      0    1   * Illegal * 1                                           0      1      1    0   2nd State Long Read                                                                        0                                           0      1      1    1   2nd State Long Write                                                                       1                                           1      0      0    0   1st State Int. Vector                                                                      1                                           1      0      0    1   * Illegal * 1                                           1      0      1    0   1st State Long Read                                                                        1                                           1      0      1    1   1st State Long Write                                                                       1                                           1      1      x    x   * Illegal * 1                                           __________________________________________________________________________

                  TABLE I                                                          ______________________________________                                         MACROJUMPS                                                                     IR Bits  Condition Tested                                                      2   1      0     STC   STSB  STEZ  Comment                                     ______________________________________                                         0   0      0     --    --    --    Unconditionally Jump                        0   0      1     --    1     --    Jump if Negative                            0   1      0     --    --    1     Jump if Zero                                0   1      1     1     --    --    Jump if Carry                               1   0      0     --    0     0     Jump if Positive                            1   0      1     --    0     --    Jump if Posiive or Zero                     1   1      0     --    --    0     Jump if Not Zero                            1   1      1     0     --    --    Jump if No Carry                            ______________________________________                                    

                                      TABLE J                                      __________________________________________________________________________     LISTING OF KEYBOARD & DISPLAY SCAN PROGRAM                                     ROM 11                                                                               OBJECT                                                                   ADDRESS                                                                              CODE                                                                     IN    IN     SOURCE STATEMENT                                                  HEX   HEX    LABEL  OPCODE                                                                               OPERANDS      OPERATION                              __________________________________________________________________________     F800  72 08 7A                                                                              INIT   MOV   %NDIGIT,NXTCHR                                                                               SETS NEXT CHAR DISPLAYED TO 8          F803  72 FF 77      MOV   % FF,DEBKEY   DEBOUNCED KEY=ESCAPE CODE              F806  D5 78         CLR   BRDPOS        RESET KEYBOARD POSITION TO 00          F808  FB            TRAP  CLRDP         CLEAR SEG PAT ARRAY                    F809  D5 6D         CLR   FLAG          CLR .R109                              F80B  D5 7E         CLR   FNFLAG        CLR FUNCTION FLAG, .R126               F80D  42 04 7F      MOV   DEBNCE,FCNT   SET FCNT TO DEBOUNCE (MOVE 4 TO                                                .R127)                                 F810  A2 D0 02      MOVP  %DO,.P2       TIMER LATCH VALUE TO DO (HEX)                                                  OR 30                                  F813  A2 C3 03      MOVP  %C3,.P3       PRESCALER LATCH VALUE TO 3,                                                    SELECT INTERNAL TIMER, AND                                                     START TIMER                            F816  72 80 6C      MOV   %80,BTPAT     INIT TO LEFTMOST DIGIT                 F819  A2 10 00      MOVP  %10,.PO       MEMORY MODE TO SINGLE CHIP             F81C  A2 FF 09      MOVP  %FF,.P9       ALL OF PORT C - OUTPUTS                F81F  52 80  KYDD   MOV   %80,B         DEBKEY MARKED AS EMPTY UNTIL           F821  D6 77         XCHB  DEBKEY        NEW KEYSTROKE IS LOADED INTO                                                   DEBKEY FROM TINTR                      F823  56 80 F9      BTJO  %80,B,KYDD    SEE IF DEBKEY STILL EMPTY, IF                                                  SO LOOP                                F826  AA F8 D5      LDA   @SEGPAT(B)    LOOK UP SEGMENT PATTERN                F829  77 FF 7E 02   BTJZ  %FF,FNFLG,NOFUN                                      F82D  E0 03         JMP   FUN           IF FUNCTION INPUT                      F82F  FA     NOFUN  TRAP  STRSEG        WRITE PAT TO DISPLAY REGISTERS         F830  E0 ED         JMP   SGMT          LOOP INDEFINITELY                      F832  FB     FUN    TRAP  CLRDP         CLR SEG PAT ARRAY                      F833  B8            PUSH  A             SAVE SEGMENT PATTERN IN STACK          F834  52 04         MOV   %4,B          INITIALIZE TABLE INDEX                 F836  AA F8 E7                                                                              FUN1   LDA   @TFUN-1(B)    LOAD SEG PAT'N OF "FUN"                F839  FA            TRAP  STRSEG        STORE FUN IN SARRAY                    F83A  CA FA         DJNZ  B,FUN1        TABLE 'TFUN'STORED?                    F83C  B9            POP   A             YES: RELOAD A                          F83D  FA            TRAP  STRSEG        PUT IN SPECIFIC FUNC KEY               F83E  22 FF         MOV   % FF,A                                               F840  D0 76  FDELY  MOV   A,FUNDLY      FDELY SUBROUTINE                       F842  12 76  FDELY1 MOV   FUNDLY,A                                             F844  E6 FC         JNZ   FDELY1        LOOP UNTIL A CLEARED                   F846  FB            TRAP  CLRDP         BLANK                                  F847  E0 D6         JMP   SGMT          RETURN TO F81F                         F849  C8            PUSH  B                                                    F84A  B8            PUSH  A                                                    F848B 52 07         MOV   %NDIGIT-1,B                                          F84D  8A 00 6D                                                                              STSEG1 LDA   @SARRAY-1,(B)                                        F850  AB 00 6E      STA   @SARRAY(B)                                           F853  CA F8         DJNZ  B,STSEG1                                             F855  D9 6E         POP   SARRAY                                               F857  C9            POP   B                                                    F858  0A            RETS                RETURN FROM SUBROUTINE                 F859  B8     TINTR  PUSH  A             SAVE A DURING SERVICE ROUTINE          F85A  C8            PUSH  B             SAVE B DURING SERVICE ROUTINE          F85B  A2 00 06                                                                              MUXSCN MOVP  %0,CHARPT                                            F85E  32 7A         MOV   NXTCHR,B      INDEX OF NEXT DIGIT TO BE                                                      DISPLAYED PUT IN B                     F860  AA 00 6D      LDA   @SARRAY-1(B)                                         F863  82 08         MOVP  A,SEGMPT                                             F865  8A 00 6C      LDA   @BTPAT                                               F868  82 06         MPVP  A,CHARPT                                             F86A  80 04  SRCH   MOVP  COLNPT,A      LOAD ANY SWITCH CLOSURES               F86C  D0 7D         MOV   A,ROWPAT      SAVE ROW PATTERN                       F86E  72 04 7C                                                                              SRCH1  MOV   %NCOLS,ROWCNT NCOLS LOOPS THRU NXTLOC                F871  76 FF 78 13   BTJO  % FF,BRDPOS,NXTLOC                                                                           BRDPOS=0 IF SCANNING F KEY                                                     LOCATION                               F875  76 80 7D 08   BTJO  % 80,ROWPAT,TEMP1                                                                            F KEY NOT DOWN                         F879  DA 7F 2B      DJNZ  FCNT,SRCH5    NOT DEBOUNCED YET                      F87C  72 FF 7E      MOV   % FF,FNFLAG   F KEY DET & DEBNCD                     F87F  E0 26         JMP   SRCH5                                                F881  D5 7E  TEMP1  CLR   FNFLAG                                               F883  42 04 7F      MOV   DEBNCE,FCNT                                          F886  E0 1F         JMP   SRCH5                                                F888  76 80 7D 1B                                                                           NXTLOC BTJO  % 80,ROWPAT,SRCH5                                                                            ONE = NO KEY DOWN                      F88C  72 FF 6D      MOV   % FF,FLAG     AT LEAST ONE KEY DETECTED IN                                                   THE CURRENT SRCH                       F88F  12 7B         MOV   DETKEY,A                                             F891  42 78 7B      MOV   BRKPOS,DETKEY                                        F894  15 7B         XOR   DETKEY,A                                             F896  E2 05         JZ    SRCH3                                                F898  42 04 79      MOV   DEBNCE,SUCCRD                                        F898  E0 0A         JMP   SRCH5                                                F89D  12 79  SRCH3  MOV   SUCCRD,A                                             F89F  E2 06         JZ    SRCH5         IF SUCCRD = 0                          F8A1  Da 79 03      DJNZ  SUCCRD,SRCH5                                         F8A4  42 7B 77      MOV   DETKEY,DEBKEY TO MARK NEW KEY CLOSURE                F8A7  D3 78  SRCH5  INC   BRDPOS                                               F8A9  DE 7D         RL    ROWPAT        TO LOOK AT NEXT COLUMN                 F8AB  DA 7C DA      DJNZ  ROWCNT,NXTLOC                                        F8AE  D2 7A  SRCH6  DEC   NXTCHR                                               F8B0  DC 6C         RR    BTPAT                                                F8B2  E7 14         JNC   SRCH9                                                F8B4  72 08 7A      MOV   %NDIGIT,NXTCHR                                       F8B7  D5 78         CLR   BRDPOS        RESET BRDPOS TO ZERO                   F8B9  12 6D         MOV   FLAG,A                                               F8BB  E6 03         JNZ   SRCH8         IF ANY KEYS WERE DETECTED              F8BD  72 FF 7B      MOV   % FF,DETKEY   CHANGE DETKEY                          F8C0  D5 6D  SRCH8  CLR   FLAG                                                 F8C2  22 76         MOV   %FUNDLY,A                                            F8C4  E2 02         JZ    SRCH9         USED BY TEST FUNCTION                  F8C6  D2 76         DEC   FUNDLY                                               F8C8  C9     SRCH9  POP   B                                                    F8C9  B9            POP   A                                                    F8CA  0B            RETI                                                       F8CB  22 00         MOV   %BLANK,A                                             F8CD  52 08  FILD   MOV   %NDIGIT,B                                            F8CF  AB 00 6D                                                                              TCLR   STA   @SARRAY-1(B)                                         F8D2  CA FB         DJNZ  B,TCLR                                               F8D4  0A            RETS                                                       __________________________________________________________________________      F8DF to F8E7 is lookup table for SEGPAT: the base for segment patterns         F8E8 to F8EB is table accessed to point out FUN                                FFF4 is trap 5, contains address F849 for STRSEG, store segment                FFF6 is trap 4, contains address F8CB for CLRDP, clear display                 FFFA contains address F859 for TINTR, timer interrupt routine                  FFFC contains address F800 for initillization subroutine                 

TABLE K Definition for Program of TABLE J

CHARPT=.P6=Port B; an 8-bit port used to enable, one at a time, the individual characters of the eight-character, seven-segment display, strobing the rows of the matrix keyboard at the same time.

SEGMPT=.P8=Port C; and 8-bit port to enable the seven segments and decimal point of the display.

COLNPT=.P4=Port A; five high-order bits or port A used as inputs from the keyboard return lines. Assumes a key down in the currently enabled row returns a low (zero) level.

CLRDP=Trap 4 of instruction set; writes blank characters into all display.

STRSEG=Trap 5 of instruction set; loads segment pattern from look-up table.

NDIGIT=8; the number of digits in the display.

NROWS=5; the number of rows in the keyboard matrix.

NCOLS=4; the number of columns in the kayboard matrix.

DEBNCE=4; number of scans used for debounce.

BLANK=00; code used to blank display characters.

MASK=1F; bits relevant to ENACC routine.

FCNT=.R127; register in RF used as the function debounce counter.

FNFLG=.R126; register in RF used as flag to indicate function.

ROWPAT=.R125; register in RF used to hold input pattern being rotated thru CY.

ROWCNT=.R124; register in RF used to count number of bits rotated through CY.

DETKEY=.R123; register in RF used to hold the position of last detected key.

NXTCHR=.R122; register in RF used in the position of next character to be displayed.

SUCCRD=.R121; register in RF used in the number of successive reads of same key.

BRDPOS=.R120; register in RF used as the keyboard position currently being scanned.

DEBKEY=.R119; register in RF used to carry the position of debounced key from MUXSCN routine back to background program.

FUNDLY=.R118; register in RF used to hold non-zero when display in progress; the next 8 registers (.R117 to .R111) hold the display segment patterns.

SARRAY=.R110; register in RF used to hold the base of register array for display pattern.

FLAG=.R109; register in RF used as flay to set when at least one key is detected in current search.

BTPAT=.R108; register in RF used to hold pattern to energize specific digit.

INIT=address R800=initialize subroutine to initialize the system.

SGMT=address F81F=routine to check for any new keystrokes detected. Translate each keystroke into a segment pattern and write it into the appropriate display register.

KYDD=Keyboard input subroutine. Returns after a new keystroke has been detected and debounced. Encoded value of key (rather than its position in switch matrix) is returned in A.

FUN=Function subroutine. This subroutine is entered when the function key is depressed in conjunction with another key. It points out FUN X, wherein X is the other key which is pressed.

FDELY=subroutine which hangs up for the number of complete display searches equal to the contents of A when called.

STRSEG=address F849=subroutine to enter contents of A into the rightmost digit and shift everything else one place to the left.

TINTR=Timer interrupt subroutine; call made to location FFFA when timer times out. This causes the display refresh and keyscan routine to be called periodically.

MUXSCN=multiplex scan routine; multiplexes the 8-segment displays. Each call causes the next character to be displayed, according to the contents of the SARRAY register array. MUXSCN should be called at least every millisec or so.

SRCH=Keyboard search routine. During MUXSCN, when next character is being displayed, with the current row energized, check if there are any inputs. A keydown returns-low level.

                                      TABLE L                                      __________________________________________________________________________     LISTING FOR TEST PROGRAM                                                       RAM  Object                                                                    12   Code                                                                      Hex  In    Source Statement                                                    Address                                                                             Hex   Label Opcode                                                                              Operands                                                                              Operation                                         __________________________________________________________________________     0B   7D 02 7D                                                                             LOOP  CMP  %02, AL                                                                               If Address = F902 (CRCADR),                       0E   E6 OD       JNZ  NOTCRC then increment 2 bytes.                           10   7D F8 7C    CMP  %F9, AH                                                  13   E6 08       JNZ  NOTCRC                                                   15   78 02 7D    ADD  %2, AL                                                   18   79 00 7C    ADC  %0, AH                                                   1B   E0 EE       JMP  LOOP                                                     1D   12 7C NOTCRC                                                                               MOV  AH, A  If MSB of address increments                      1F   E2 29       JZ   CHKDON past FF, then all of ROM has                      21   9A 7D       LDA  *AL    been processed, so jump to                        23   15 7E       XOR  QH, A  CHKDONE. Otherwise, go to                         25   42 7F 7E    MOV  QL, QH BUILDF.                                           28   C5          CLR  B                                                        29   B6          XCHB A                                                        2A   72 08 02    MOV  %8, R2                                                   2D   65    BUILDF                                                                               XOR  B, A   Process current CRC QH, QL with                   2E   CF          RLC  B      current data byte (B).                            2F   DA 02 FB    DJNZ R2, BUILDF                                               32   D0 7F       MOV  A, QL                                                    34   7C 02 7F    MPY  %2, QL                                                   37   45 00 7E    XOR  A, QH                                                    3A   7C 40 7F    MPY  %64, QL                                                  3D   45 00 7F    XOR  A, QL                                                    40   45 01 7E    XOR  B, QH                                                    43   D3 7D       INC  AL                                                       45   79 00 7C    ADC  %0, AH                                                   48   E0 C1       JMP  LOOP                                                     4A   A2 55 08                                                                             CHKDON                                                                               MOVP %55, CPORT                                                                            Check done; the test loop is                      4D   A2 FF 09    MOVP %FF, CDIR                                                                             done; set C port as output and                    50   8A F9 02    LDA  @F902  apply hex 55 or 01010101 to C                     53   1S 7E       XOR  QH, A  port as a signal.                                 55   82 0A       MOVP A, DPORT                                                 57   A2 FF 0B    MOVP %FF, DDIR                                                5A   8A F9 03    LDA  @F903                                                    5D   1S 7F       XOR  QL, A                                                    5F   82 08       MOVP A, CPORT                                                 __________________________________________________________________________      Definitions:                                                                   QL = R127                                                                      QH = R126                                                                      AL = R125                                                                      AH = R124                                                                 

What is claimed:
 1. A microcomputer device formed in a single semiconductor integrated circuit (10) with internal self-test of instruction code, comprising:a CPU having an ALU (14) with a plurality of address/data registers (15) and bus means (16) for accessing the registers and input/output for the ALU, control means including an instruction register (IR) for defining the operation of the CPU in response to multi-bit instruction code words, said control means including means (17) for generating control signals from said instruction code words which are transferred into said instruction register (IR), program storage means (11) in the integrated circuit for permanently storing a plurality of instruction code words and a check-code representation of all of the bits in all of said plurality of instruction code words, read/write storage means (12) in the integrated circuit (10) for temporarily storing data or storing other instruction code words, means for transferring (MD) sequences of said instruction code words into said instruction register either from said program storage means (11) or from said read/write storage means (12), said CPU and control means accessing said other instruction code words from said read/write memory (12) to perform a sequential operation on all of the bits in all of said plurality of instruction code words and to generate a first output (30) from the device if a result of such operation corresponds to said check-code representation and a second output (30) from the device if such result does not correspond to said check-code representation.
 2. A device according to claim 1 wherein said program storage means includes a semiconductor read-only memory array storing said plurality of instruction code words.
 3. A device according to claim 2 wherein said read/write storage means is a semiconductor read/write array and said CPU transfers addresses from said address/data registers to either the read/write memory array or the read-only memory array via said bus means.
 4. A device according to claim 3 wherein operation of said CPU is defined by instruction code words of N bits in width transferred into said instruction register, and said address/data registers and said bus means are N bits in width, and wherein instruction code words are stored in said read-only memory array or read/write memory array as words of N bits in width.
 5. A device according to claim 4 wherein said other instruction code words in said read/write memory array and said check-code representation are addressed from said CPU using said address/data registers and bus means.
 6. A method testing an integrated semiconductor device of the type containing a digital processor having a plurality of different processor functions and a plurality of multibit instruction words defining the different processor function stored in said device, comprising the steps of:storing on said device a multibit code representing a commulative function of all of the bits in all of said plurality of multibit instruction words, transferring into said device a test routine made up of instruction words, and storing said test routine temporarily in said device, activating the device using said test routine to perform arithmetic or logic operations via said digital processor on all of said plurality of multibit instruction words to produce a result, producing a first electrical signal at output terminals of said device is said result corresponds to said multibit code, and producing a second electrical signal at output terminals of said device if said result does not correspond to said multibit code.
 7. A method according to claim 6 wherein said step of activating the device causes the digital processor to operate on words N bits wide accessed from a read/write memory on said device, where N is an integer, and wherein each of said plurality of multibit instruction words is N bits wide and accessed from a read-only memory on said device.
 8. A method according to claim 6 wherein the step of transferring into said device is performed by executing a loading routine defined by instruction words stored external to the device.
 9. A method according to claim 8 wherein said multibit code representing a cummulative function is in the format of the instruction words and is stored in a read-only memory on the device.
 10. A method according to claim 9 including the step of producing a sequence of microcode controls in said device said produced for each of said instruction words. 